我认为问题的关键就在于“出售时间”这个概念。

And I think the key here is the selling of time concept.

youdao

问题的关键就在于你要把你所写下来的目标放在一个醒目的，随时可以看到的地方。

The key is to put your written goals in a visible place where you will see them during your day.

youdao

问题的关键就在于这些压电材料是否可以控制，你必须保证所有材料的正负极一致。

"A key issue for piezoelectric materials is order," he says. "You need to make sure all the positives and all the negatives are pointing in the same direction."

youdao