元素周期表中16号元素和4号元素的原子相比较，前者的下列数据是后者4倍的是[ ]
A．最外层电子数
B．次外层电子数
C．电子层数
D．中子数
答案：B
—Teenagers shouldn't spend too much time playing computer games.
—_____. We should make good use of our time.[ ]
A. I disagree
B. That's all right
C. I agree
D. I'm afraid so
专变终端对脉冲输入宽度的要求为多少秒？
