Dolphins form extremely complicated allegiances and _______ continually change.

Enmities that

The sentence has a main subject and verb. Also, there is a connector and with one of two options. The first option is a noun; therefore, the needed option must also be a noun. 1. It is not (D) because it starts with a connector. 2. It is not (C) because it has a verb. 3. It is not (B) because it has a verb 4. It is (A)