Why this works

During goes before a thing (during the week). While goes before a person and an action (while we eat). Both say that something happens at the same time as another thing. Say during the lecture, not while the lecture.

Examples

• My sister made two good friends during the first week.

• The professor showed a video while the students listened to the lecture.

Why this works

By means on that time or before it. It is for a last day (by Friday). Until means all the time up to that moment, and then it stops (until nine). Say send it by Thursday, not until Thursday.

Examples

• We must hand in the form by Friday, but the library is open until nine.

• The library on campus stays open until midnight.

Why this works

For says how long something goes on (for three years). Within says before that time is finished (within a week). Say runs for two hours, not runs within two hours.

Examples

• The course lasts for three years, and you must choose a module within a week.

• You must pay the school fee within ten days.

Why this works

At the end of goes before a thing and means the last part (at the end of the term). In the end stands alone and means finally. Say In the end I chose, not At the end I chose.

Examples

• There is a big test at the end of the term.

• I looked at ten courses, and in the end I chose chemistry.