A (A) dolphin is (B) a (C) very intelligent and (D) lovely animal.

The word "a" in option (B) is unnecessary. The correct sentence is: A dolphin is a very intelligent and lovely animal. However, if the question is about the article "a" in option (C) or (D), it would be more grammatically correct to use "and a lovely" instead, making it: A dolphin is a very intelligent and a lovely animal. But in standard English, we often don't use the second "a" before "lovely."