(2013·安徽省芜湖三校一模)A recent study has found that the number of smokers ________ sharply over the past five years.

A．is increasing

B．are increasing

C．has been increasing

D．have been increasing

咏叹调《今夜无人入睡》是选自写的歌剧《　　　　　》，这部歌剧描写了一个发生在中国元朝都城北京的故事。