某报社做了一次关于“什么是新时代的雷锋精神”的调查,在A,B,C,D四个单位回收的问卷数依次成等差数列,且共回收1 000份,因报道需要,再从回收的问卷中按单位分层抽取容量为150的样本,若在B单位抽取30份,则在D单位抽取的问卷份( )
A:60
B:200
C:400
D:140
阅读下面的内容,并对后面的句子作出判断。
It isn't a small shop(商店). It is near our home. It looks very lovely. My parents and I often go shopping. I buy books, rulers and pens in the shop. My parents buy milk , bread and eggs. The service(服务) is very good. We all like the shop.
人体消化食物和吸收营养物质的主要器官是( )
如图所示是家庭电子式电能表的表盘,其示数是____KW•h,表盘上标有“3200imp/kW•h”,表示每消耗1kW•h的电能,指示灯闪烁3200次,若家庭电路中只有一台电热水器在工作,该电能表的指示灯在4min内闪烁320次,则该热水器的实际功率是____W.