Read the following paragraphs, and find the main idea or major detail of each paragraph, and choose the correct answer. 
I.     
Culture itself must be transmitted, and the most effective way is through the family. Parents teach their children the ideas and   traditions they obtained from their own parents. For this reason the family became increasingly important; the practical  applications of cultural traditions, such as hunting for food, rearing children and tending the sick, may have been the obvious methods to use when more than one family came together in a joint activity.
Question : what's the main idea of this paragraph?
A、 Parents play a vital role in cultural transmission.
B、Culture itself must be transmitted.
C、The practical applications of cultural traditions may have been the obvious methods to use when more than one family came together in a joint activity.
D、 Parents teach their children the ideas and traditions they obtained from their own parents.