下列选项中,属于分馏塔冲塔现象的是()。
A、分馏塔温度快速下降
B、分馏塔温度没变化
C、分馏塔温度快速上升
D、无法确定
参考答案:C
在透明塑料薄膜上滴一滴小水珠(直径约5mm),透过水珠看纸上的字,这时水珠相当于一个______透镜,在水珠比较接近纸面时,看到的是放大的______像.
Not once ________ to Michael that he could one day become a top student in his class.
A.occurred it
B.it did occur
C.it occurred
D.did it occur