当原子的最外层电子数发生改变时，会引起改变的是（　　）

A．相对原子质量

B．元素种类

C．中子数

D．化学性质

短文改错

I used to feeling pressured to do well in exams. I was such afraid of falling behind that I kept thinking about studying every minute of the day. The pressure makes me out of breath. To my disappointed, the more worried I was about my studies, the less effective I became. Later, I realized I just took pressure too serious. So I tried taking things easy by taking part in various activity out of class, enjoying music and even daydreaming about fun things.

To my delight, this worked! Gradually，I became more anxious about exams and began to take pleasure in my studies. Pressure cannot avoided. What counts is how to deal with properly, but above all, how to turn it into pleasure or challenge.