If you start a sentence with' are you...'than the verb after it must always be in -ING form for example going, eating, sleeping etc. In your case the correct question would be: Are you enjoying your dinner? And then you would simply answer :'yes, it i very nice or yes, it is delicious'etc.Simple-:))Kamila

And in everyday English, the answer would be "Yes, I like it very much. It tastes delicious."

it is just one of the exercises in my english book. thank you for your specific explanation.

And the best answer is D, especially if "dinner" means "the food." Or C, if dinner means "the act of eating food with other people and perhaps entertainment." But, in fact, none of the answers would be common in everyday English. We would normally ask a friend or guest: "How do you like your dinner? Does it taste good?"

sorry, wrong typing...and could you tell me which is the correct answer?