定时基准信号的传输方式。

In every school there is a "top" crowd that sets the pace, while the others follow their lead. Let’s say the top crowd decides that it is smart to wear bright red sweaters. Pretty soon everybody is wearing a bright red sweater.
There is nothing wrong with that, except the fact that on some people bright red sweater is extremely unbecoming. The situation can even become dangerous, if the top crowd decides that it is smart to drink or to drive cars at seventy miles an hour. Then the people who follow the lead are endangering their lives. They are like the sheep being led to the butcher.
Now, chances are that you have come across situations like these more than once in your life; chances are that one time or another you probably did something you knew to be wrong. You may have excused yourself by saying, "Gee, the crowd does it. " Well, let the crowd do it, but don’t do it yourself. Learn to say "No".
Develop your own standards and your own judgment. If you know the crowd is planning something you disagree to, have the courage to bow out mannerly. You’ll have the satisfaction of standing on your own two feet.

The author doesn’t think it good wearing red sweaters if ______.

A. the crowd does it
B. you can’t afford them
C. you don’t look good in red
D. the situation isn’t safe