My favourite aminal is the dog 。dog不再是表示是一只狗，而是表示狗这一类动物所以应该加the
My favourite animal is dog .这是正确的.我最喜欢的是狗,狗在这里为泛指,指狗类.“animal ”not “aminal”
应该是My favourite aminal is dogs
应该是 My favourite animals are dogs.
