Animals become indifferent to their young as soon as their young can look after themselves, but human beings, owing to the length of infancy, find this less easy.
A.Animals are not different with their children when their children grow up, but human beings are the same with their children.
B.Animals do not care about their children as soon as they can look after themselves. This is similar to human beings.
C.Animals do not care about their children as soon as they can look after themselves,but it is difficult for human beings to do so, because the period of infancy is too long.
D.Both animals and human beings are indifferent to their children as soon as their children grow up, but the infancy of human beings is too long.
正确答案是C