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C1 Advanced Grammar • 12 Mins Theme: Space Weather & Magnetic Fields

Continuous Modals & Infinitives for Speculation

Master continuous patterns (must be doing, may have been doing, appears to be doing) to make precise guesses about actions in progress.

💡 How to use this lesson

For Teachers

Set 12 minutes for this core grammar module in class or as homework. Guide learners through the 4 core rules first, then check their answers together using the auto-graded key provided below.

For Learners

Read the rule table carefully and look closely at the underlined examples. Complete the 12 practice tasks below (from easy to hard) to test how well you can guess about actions in progress.

📖 Grammar Rule Guide

Learn how each continuous speculation form works with simple explanations and space weather examples.

Row 1 Modal + be + -ing (Ongoing Speculation)

Use this pattern when you make a guess about something happening right now. Use must for a strong guess, may or might for a weak guess, and can't for a strong guess that it is false.

🔹 The satellite must be losing power, because the screen keeps going dark.

🔹 High-energy radiation may be surging near the earth's atmosphere right now.

Row 2 Modal + have been + -ing (Past Continuous Speculation)

Use this pattern when you guess about a continuous action that happened before a past moment. It shows a slow process that took time in the past.

🔹 The storm may have been building for days before anyone noticed it.

🔹 Hot plasma must have been leaking from that sunspot all week.

Row 3 Seems / appears + to be -ing

Use seems or appears with to be -ing or to have been -ing to make a guess based on evidence. Seem and appear are not modal words, so never put a modal word before seem or appear.

🔹 The magnetic field appears to be changing more quickly than before.

🔹 The polarity of the sunspot seems to have been shifting over the past month.

Row 4 Strong guesses that something is not true

To guess strongly that something is NOT true, always use can't or couldn't. Never use mustn't for a guess. After any modal, always write be -ing, never just -ing or to be.

🔹 That signal can't be coming from the old tower, because the tower has no power.

🔹 The main power transformer couldn't have been failing before the solar eruption hit.

⚡ Critical Rule Alert

Never use "mustn't" for negative speculation!

When you are sure something is NOT happening or was NOT happening, use can't be... or can't have been.... In English, mustn't is strictly for prohibition (rules/laws), not for making a logical guess.

⚖️ Common Mistakes to Avoid

✅ Correct Usage

The grid shield can't be failing right now.
The aurora seems to be changing color.
High radiation may be surging.

⚠️ Incorrect Usage (Avoid)

The grid shield mustn't be failing right now.
The aurora must seems to be changing color.
High radiation may happening.

Interactive Practice

12 items across 4 task types • Easy to Hard

📝

Part 1: Choose the correct sentence

Question 1 (sure)

Choose the correct sentence to express high certainty about a system glitch that is happening right now:

____ a. The solar eruption must be causing the glitch. ____ b. The solar eruption must have been causing the glitch.

Question 2 (sure not)

Choose the sentence that correctly expresses negative speculation about an aurora observation:

____ a. The aurora mustn't be appearing at this latitude. ____ b. The aurora can't be appearing at this latitude.

Question 3 (observation)

Choose the correct infinitive speculation pattern:

____ a. The transformer appears to be overheating. ____ b. The transformer may appears to be overheating.

Part 2: Rewrite fact and certainty as one speculation sentence

Question 4 (sure)

Fact: The plasma stream is expanding.

Certainty: almost sure. (Use: must be)

____ (Type your full sentence here...)

Question 5 (possible)

Fact: The magnetic polarity was reversing for hours.

Certainty: possible. (Use: may have been)

____ (Type your full sentence here...)

Question 6 (sure not)

Fact: The grid shield was not operating during the surge.

Certainty: almost sure it is not true. (Use: can't have been)

____ (Type your full sentence here...)

Part 3: Fill in the gaps with the correct verb form

Question 7 (sure)

Look at the sensors! Intense radiation ____ (surge) through the atmosphere right now.

Question 8 (possible)

Scientists think the sunspot ____ (grow) in size long before the explosion occurred.

Question 9 (process)

According to new data, the earth's magnetic shield ____ (act) unstable lately.

Part 4: Correct the error in a short message

Question 10 (error)

💬 "Hey! The power grid just went out. A massive solar surge musting be hitting us!"

Write the corrected verb phrase:

____ (Type correct phrase...)

Question 11 (error)

💬 "Did you see the green lights? The aurora seems fading, so hurry and look outside!"

Write the corrected verb phrase:

____ (Type correct phrase...)

Question 12 (error)

💬 "The lab team claims the transformer might to have been glitching all night."

Write the corrected verb phrase:

____ (Type correct phrase...)

Continuous and Perfect-Continuous Modals

Continuous Modals & Infinitives for Speculation

💡 How to use this lesson

For Teachers

For Learners

📖 Grammar Rule Guide

Never use "mustn't" for negative speculation!

⚖️ Common Mistakes to Avoid

✅ Correct Usage

⚠️ Incorrect Usage (Avoid)

Interactive Practice

Part 1: Choose the correct sentence

Part 2: Rewrite fact and certainty as one speculation sentence

Part 3: Fill in the gaps with the correct verb form

Part 4: Correct the error in a short message

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