自行车链条需要与齿轮的轮齿紧密咬合才能正常工作。

The chain must fit tightly with the ___cogs on the gear for the bike to work properly.

在大公司里，他觉得自己只是一个小齿轮，毫无影响力。

In the big company, he felt like just one of many ___cogs with no real influence.