The trick is to generate the highest frequency possible but keep the averageduty cycle constant.
关键是产生最高频率的可能性，还能保持平均的占空比常数。
2
They believed that because good fortune had endowed them with better than average opportunity, they had a duty to perform in their communities.
他们认为他们有责任在自己的群体中履行自己的职责，因为好运给了他们比一般人更多的机会。
3
Those who make the connection between size and safety point out that after slimming down in the 1980s, the average American light-duty vehicle has bulked up over the past two decades.