阅读理解。
Once there were three old men. They were rather forgetful. They always forgot what they were doing.
One of them said, "I always wonder if I want to buy a coat or a pair of socks.
The second old man said, "I often forget if I should put something in or take something out of the fridge as soon as I open its door."
"I am even more forgetful than both of you." Said the last old man ,and he knocked at the table. Then he turned to the other two men and asked, "Who just knocked at the table?"
1. The second old man said .
A. he forgot where he should go
B. he forgot whether he wanted to put something in the fridge
C. he forgot his key
2. The first old man forgot .
A. what he wanted to buy
B. where he wanted to go
C. what he should bring
3. The third old man said .
A. he was less forgetful than the others
B. he was more forgetful
C. he was remembering what he was doing
4. Who is the most forgetful?
A. The first old man
B. The second old man
C. The third old man
5. From the story we can know .
A. None of them are young
B. None of them is forgetful
C. The second old man is most forgetful
，在竖直方向存在如图乙所示交替变化的电场（竖直向上为正），电场强度E0大小为
，空间中有一倾角为θ的足够长的光滑绝缘斜面，斜面上有一质量为m，带电荷量为-q的小球，从t=0时刻由静止开始沿斜面下滑，设第7s内小球不会离开斜面，重力加速度为g，求：
