为什么尿素、铵盐、双缩脲等无机氮化物可用来补充反刍家畜饲料氮源的不足？

Helen is a middle student.She lives far from _____ school,so she usually takes the bus to school.She _____ to school at about six thirty _____ the morning.She _____ want to be late.
The first class _____ at eight o’clock.There are four classes in the morning and two in the afternoon.She doesn’t go home _____ lunch.She has it at school.
Helen learns Chinese,math,biology,PE and some other _____.She works very hard,and she _____ math very much _____she thinks it’s very interesting.
In the evening,Helen usually does her homework and sometimes she watches TV.She goes to _____ at ten o’clock.

小题1:	A．her B．his C．she D．he

小题2:	A．go B．come C．goes D．get

小题3:	A．in B．on C．at D．of

小题4:	A．isn’t B．doesn’t C．don’t D．aren’t

小题5:	A．start B．has C．have D．starts

小题6:	A．at B．of C．for D．with

小题7:	A．subjects B．sports C．shows D．collections

小题8:	A．likes B．like C．isn’t D．doesn’t like

小题9:	A．so B．but C．because D．or

小题10:

A．school B．work C．bed D．class