锅炉汽包水位过低,一定能起到提高水位调节作用的是()。
A.提高给水压力
B.提高给水压力使流量增大
C.开大液位控制阀的副线阀
D.停止锅炉排污
参考答案:B, D
缺词填空(5分)
We usually buy things in a shop, a market or a supermarket. Shopping always takes too much t________ . We have to walk around for a long time to look f________ the things we want. Sometimes we have to c________ many heavy shopping bags. We’re always very tired after s_________. Now it’s different from that in the past(过去). We can do many things at h________, we don’t need to go to the shop. We can buy many good and c_______ things on the Internet(因特网), they look nice but don’t cost much. It seems easy and quick, b_______ it sometimes brings us some trouble(麻烦). The clothes you buy on the Internet are d________ from what you want, or the size is too s_______ or too big. You may see many people wear the same clothes in the street. Do you know why? B________ they all buy clothes on the Internet. How interesting!
在平面直角坐标系中,入射光线经过y轴上点A(0,3),由x轴上点C反射,反射光线经过点B(-3,1),则点C的坐标为______.