卡门旋涡式空气流量计按其检测方式可分为（）和（）。
参考答案：光学检测方式；超声波检测方式
—There _____ lots of plants here. But now I can't see any.
—That's the problem. To solve it, we _____ grow trees here.[ ]
A. used to be; are going to
B. are used to be; will
C. used to are; are going to
D. are used to; will
