somewhere down 在句里是什么成分

地点副词
具体如下：
地点副词指表示地点的副词和表示位置关系的副词统称为地点副词.常见的这类副词有：
表示地点的：here,there,home,upstairs,downstairs,anywhere,everywhere,nowhere,somewhere,abroad,elsewhere等.
表示位置关系的：above,below,down,up,out,in,across,back,along,over,round,around,away,near,off,on,inside,outside,past等.
在表示位置关系的副词中,有些副词也可用作介词(如：above,over,beyond,around,below,down,up,in,along,near,off,on,past等),在没有宾语时就是副词,有宾语时就是介词,如：
Come in,please.(副词)
They live in the next room.(介词)
Let's take along.(副词)
Let's walk along this street.(介词)
She looked around.(副词)
They sat around the table.(介词)
Let's go on with the work...(副词)
What subject will you speak on?(介词)
四、地点副词在句中的位置
地点副词常放在动词后面,如果是及物动词,一般就放在宾语后面.如：I remember having seen him somewhere.
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地点副词和时间副词并列使用时,一般要把地点副词放在时间副词之前.如：
We had a meeting here yesterday.
He did the work carefully here yesterday.
如果地点状语很长时,也可以放在时间状语之后.如：
He was born in 1940 in a small village at the foot of Mount Tai.
五、地点副词常可以用作表语
副词可以用作表语,主要是地点副词,时间副词和其他副词有时也可以用作表语.如：
They are inside.他们在里面.
How long will she be away?她要离开多久?
When will you be back?你什么时候回来?
You haven't been around much.你很少到这边来.
He'll be round in an hour.他一个小时内就到.
Now autumn is in.秋天来了.
I must be off now.我得走了.
We are behind in our plan.我们落在计划后面了.