Answer:
5. je jette
6. ils achètent
7. nous devons
Explanation:
jeter requires one to double the t in the je, tu, il/elle/on, and ils/elles conjugations and is otherwise conjugated as an -er verb
acheter requires an accent in je, tu, il/elle/on, and ils/elles as written in the answer
devoir is an irregular conjugation and must be memorized
