Here are the corrected sentences:

1. 20 percent of the forest **has** been destroyed lately.
=> 20 percent of the forest **has** been destroyed lately.

2. The witnesses saw that most of the fire in the hills **had been** extinguished.
=> The witnesses saw that most of the fire in the hills **had been** extinguished.

3. Some of the animals from the zoo **were** released into the animal preserve.
=> Some of the animals from the zoo **were** released into the animal preserve.

4. All of the students in the class taught by Professor Roberts **are** required to turn in their term papers next Monday.
=> All of the students in the class taught by Professor Roberts **are** required to turn in their term papers next Monday.

5. Half of the food that we are serving to the guests **is** still in the refrigerator.
=> Half of the food that we are serving to the guests **is** still in the refrigerator.

6. We believe that some of the employees **are** going to be devoted to quality control.
=> We believe that some of the employees **are** going to be devoted to quality control.

7. It is impossible to believe that somebody actually **adores** that man.
=> It is impossible to believe that somebody actually **adores** that man. (or "admired" for past tense consistency)

8. Each of the doctors in the building needs to have a separate reception area.
=> (This sentence is already correct.)

9. The president felt that no one **was** better suited for the position of chief staff advisor.
=> The president felt that no one **was** better suited for the position of chief staff advisor.

10. Everybody participating in the fund-raiser **is** to turn in the tickets by 8.00.
=> Everybody participating in the fund-raiser **is** to turn in the tickets by 8.00.

These corrections address the subject-verb agreement and correct tense usage.