Can you pls help me complete exercise 8

Exercise 8. Given below are five groups of sentences. Each group consists of three sentences, one of which is unacceptable. Cross (X) the sentence which is unacceptable and rewrite it correctly: (oral discussion also)
1. (a) They are having their dinner. (    )
(b) They are fully agreeing to our proposal. (    )
(c) She is thinking hard on this issue. (    )

2. (a) This drum is containing very little oil. (    )
(b) Are you sure you are not forgetting some points? (    )
(c) Please don't forget to attend tomorrow's rehearsal. (    )

3. (a) Are you listening to the talk carefully? (    )
(b) Are you still having problems with geometry? (    )
(c) I am doubting the truth of this statement. (    )

4. (a) This medicine tastes bitter. (    )
(b) Are you understanding what I am explaining? (    )
(c) She weighs 43 kg. (    )

5. (a) Do you hear any unusual sound? (    )
(b) She is not believing in God. (    )
(c) She appears to have lost something. (    )