Reading on-line just takes a little getting used to.

在线阅读只需要习惯它。

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get used to something只适应某东西，上句中的getting used to是个动名词短语，把整一块都看作个名词就行了。It takes some time to get used to a new job.适应一份新的工作需要些时间。

例句：
It is very difficult to get used to working with heavy smokers.和烟瘾很重的人一同工作是非常难适应的。