You need a key to get in.

你需要钥匙才能进去。

He used a key to open the door.

他用钥匙开启了门。

He used a key to unlock the door.

他用钥匙解锁了门。

She used a key to lock the drawer.

她用钥匙锁上了抽屉。

You need a key to unlock this file.

你需要一个密钥来解锁这个文件。

The door is locked; you need a key to open it.

门被锁住了，你需要钥匙才能打开。

Finding profitable niches can be a key to a successful business.

找到有利可图的小众市场是成功企业的关键。

Education is a key to improving the lives of underprivileged families.

教育是改善贫困的家庭生活的关键。

White matter is a key to the development of language and reading skills.

白质是语言和阅读技能发展的关键。

To those who say that money can't buy happiness I answer that money is a key to happiness.

对于那些说金钱买不到幸福的人，我的回答是金钱是幸福的关键。