Here are the correct answers for the sentences provided:

2. Paul (already / finish) **has already finished** his work for the day.

3. His cousin Tam (visit) **visited** the Grand Canyon last year and it (be) **was** truly breathtaking.

4. We (learn) **have learned** so much since we (start) **started** this course.

5. The bakery (not / sell) **has not sold** out of their delicious croissants so far, so I should hurry and get one.