哺乳仔猪一般在（）日龄开始补饲。
A、7-10
B、8-11
C、9-12
D、10-13
参考答案：A
It’s those _____ experience ups and downs with us_____ are real friends.
A．that, that
B．who, that
C．that, which
D．that, who
如何判断哪一层是有机物？哪一层是水层？
