下列有关气温变化规律的说法,正确的是[ ]
A.气温随纬度的增加而升高
B.气温随纬度的增加而降低
C.气温不随纬度发生变化
D.气温变化没有一定规律
答案:B
You should understand the math problem now, you have had it ______ three times. [ ]
A. explaining
B. to explain
C. explained
D. explain
如何对填料密封进行维护?