A. for (How long . . .) vs. during (When. . .)
- for two weeks; during the winter

B. by (completion) vs. until (continuation)
- Have it done by tomorrow. Use the car until this evening.

C. between (two) vs. among (more than two)
- between the eyes; among the crowd

D. Prepositions at the end of questions
- Who did you come with? What is this for? What is it like?