牛的粗饲料应是日粮之主体,一般粗饲料应占日粮干物质的()。
A.40%--60%
B.20%--30%
C.70%--80%
D.10%--20%
参考答案:A
________ he returns to his native land.
A.It is long that
B.It is not before long that
C.It won’t be long before
D.It will be long until
乙类互补对称功率放大电路会产生( )
A.频率失真 B.交越失真C.饱和失真 D.截止失真