我的理解是，A类型的只有A这个因素在，描述A的利弊有推导过程，AC则是一定要推导到C。像这道题Some people think that children should learn paint and draw. Others believe that is a waste of time. Discuss both views and give your opinion. 前面的就要求should的好处，后面则是要求should推出waste time,如果后面换成Others believe children should not应该就又变成A类了。