Question

6. I was doubtful whether it was you. (Negetive)
7. Aren’t dogs faithful animals? ( Assertive)
8. He will never forget that experience. (Interrogative)
9. If only I were young again! (Assertive)
10. He succeeded in his attempt. (Use the noun form of Succeeded )​

Answer 1

Answer:

6. I wasn't doubtful whether it was you.

7. Dogs are faithful animals?

8. Will he never forget that experience?

9. I wish I was young again.

10. He was success in his attempt.

                  Hope it helps you^_^