简述煤粉细度及其公式。
参考答案:
1.煤粉细度指煤粉由专用筛子筛分后,残留在筛子上面的煤粉质量a占筛分前煤粉总质量的百分数。
2.公式为R=a/(a+B.×100%。
阅读理解
It is a Saturday morning, Mr Black and his child, Bill are in a big shop. The shop sells clothes and
school things. Mr Black wants to buy a new sweater for his wife. Bill would like a T-shirt. So his father
buys a green one for him. Bill wants to buy some picture books and color pencils, too. There are many
things and many people in the shop. They are men and women, old and young. They all like to buy
something there. The workers in the shop are friendly.
1. Mr Black goes to the shop with___________
A. his son
B. Mrs Black
C. his father
D. other old people
2. Mr Black is going to buy a new sweater for __________
A. Mrs Black
B. Bill
C. his friend
D. his son
3. Mr Black buys ______for Bill.
A. a T-shirt
B. a sweater
C. shorts
D. a hat
4. People in the shop are ________
A. old and young
B. men and women
C. A and B
D. young
5. Does Mr Black buy Bill picture books?
A. No
B. Yes
C. It's green
D. We don't know
为雷电流泄入大地形成通道的设备叫避雷器。