“be back”中的“back”是什么词性？

这里的“back”属于副词，表示“回来”的意思。

back
英 [bæk] 美 [bæk]
n.
背，背部;背面，反面;后面，后部;（椅子等的）靠背
vt.
使后退;支持;加背书于;下赌注于
vi.
后退;倒退
adj.
后面的;背部的;以前的;拖欠的
adv.
以前;向后地

例句：

• The photographers drew back to let us view the body    

  摄影师往后退开，好让我们查看尸体。 

• I went back to bed      

  我回到床上。 

• The rail company said it expected services to get slowly back to normal      

  铁路公司表示，其运输服务将慢慢恢复正常。 

• She handed the knife back      

  她递还刀子。 

• They wrote back to me and they told me that I didn't have to do it      

  他们回信告诉我说不必那么做。 

• Can I come back to the question of policing once again?      

  我能再回到维护治安的问题上来吗？ 

• Short skirts are back      

  短裙又流行起来了。 

• Her hair was tied back      

  她的头发扎了起来。 

• She lay back and stared at the ceiling      

  她躺下盯着天花板。 

• Nick looked back over his shoulder and then stopped, frowning      

  尼克回头看了看，又皱着眉头停了下来。 

• Meanwhile, back in London, Palace Pictures was collapsing      

  与此同时，伦敦的皇宫影业公司也正在分崩离析。 
  

• He paced back and forth      

  他来回踱步。 

• Her son was lying peacefully on his back      

  她儿子安静地仰面躺着。 

• She raised her hands to the back of her neck      

  她举起双手放于颈后。 

• He opened the back door      

  他打开了后门。 

• There was a neatly folded pink sweater on the back of the chair.      

  椅子的靠背上搭着一件叠得整整齐齐的粉色毛衫。  

  
  

back是形容词,形容回来的状态,不能在前面直接主语beback是动词,描述已经回来了,可以在前面直接加主语