如何进行营养指标的重点控制？
参考答案：
需要从动物种类、饲养管理方式、饲料组成、营养及相关学科发展的限制等因素进行重点控制
The boy was so tired that he fell asleep _____________ his mother could take off his clothes．
A．before
B．after
C．while
D．where
______是教育工作能否达到预期目的的关键。
