根据现行的国家标准，采用IS0法检验水泥胶砂强度时，所采用的水灰比为（）
A.O.50
B.O.60
C.0.65
D.0.40
参考答案：A
阅读理解。
1. Who is helping protect the environment?
A. Mrs. Gao
B. Mr. Xu
C. Miss Gao
D. Mr.Lu
2. When can people go to visit the old people in the old people’s home?
A. On Monday.
B. On Wednesday.
C. On Friday.
D. On Saturday.
3. What does the second piece of news call on people to do?
A. To stay with the poor.
B. To visit old people.
C. To help the poor.
D. To collect rubbish.
如图所示，在杨氏双缝干涉实验中，激光的波长为5.30×10-7m，屏上P点距双缝S1和S2的路程差为7.95×10-7m，则在这里出现的应是__________（选填“明条纹”或 “暗条纹”）现改用波长为6.30×10-7m 的激光进行上述实验，保持其他条件不变， 则屏上的条纹间距将___________（选填“变 宽”、“变窄”或“不变”）。
