光栅常数
参考答案：
相邻两缝中心的间距d，大小等于透光部分与遮光部分宽度值和
Sorry, I am too busy now. If I ________ time, I would certainly go for an outing with you. [ ]
A. have had
B. had had
C. have
D. had
收入水平不影响货币需求。（）
