【1】She left the keys behind her at home.【behind为介词用法】

【2】She left the keys behind at home.【behind为副词用法】

【3】She left the keys at home.【leave sth+介词短语用法】

【一】leave sth+介词短语 表示“把某物遗忘在某地”

I've left my bag on the bus.我把包丢在公共汽车上了。

【二】leave sb/sth+behind=leave behind sb/sth 有以下4种意思

【1】忘记带了某物

Don't leave any of your belongings behind.别忘了带上自己的随身物品。

【2】把…抛在后面；超过

We're going to be left behind by the rest of the world.我们将被全世界甩在后面。

Britain is being left behind in the race for new markets.英国在开拓新市场方面正被甩在后面。

【3】让某物/某人留下/留在某地方

He wasn't well, so we had to leave him behind.他身体不适，因此我们只好把他留下。

I don't want to leave anything behind. 我不想留下任何东西。

A misty rain in the morning had left behind a coolness that would stay for hours.  

早上，蒙蒙细雨带来一股清凉之意，数小时不散。

【4】永久性丢下/抛下/离开某人/某物

She knew that she had left childhood behind.她知道童年已一去不复返了。

The rebels fled into the mountains, leaving behind their weapons and supplies.

叛军丢下武器和给养，逃进了山里。

He came to Saudi Arabia, leaving behind his wife and their three children. 

他抛下妻子和三个孩子来到了沙特阿拉伯。

Many of the women had left their husbands behind and they told of their fears that they may never see them again.

这些女人中很多抛下了自己的丈夫，她们说害怕可能永远都见不到他们了。

We hear of women who run away, leaving behind their homes and families.  

我们听说有女人离家出走，扔下了家人不管。

备注：leave sb/sth+behind=leave behind+sb/sth中的behind为副词用法，如果宾语为名词，放在中间和后面都OK,如果宾语为宾格代词必须放在中间。