蓄冷器的切换时间是根据什么确定的？
参考答案：
蓄冷器的切换时间就是根据切换后冷端温差增大到控制值（最大允许温差）所经过的时间来确定的。
There isn't any difference between the two. I really don't know _________. [ ]
A. where to choose
B. which to choose
C. to choose what
D. to choose which
油菜出现只开花不结果的现象，需要施加（ ）
A．含硼的无机盐
B．含铁的无机盐
C．含硫的无机盐
D．含磷的无机盐
