About one fourth of the families in the city have private cars and this number _____ to double in five years.

A．is expecting

B．has expected

C．is expected

D．will expect

下列实验操作或方案正确的是

A．用燃着的木条区分氮气与二氧化碳

B．用酚酞溶液鉴别盐酸和氯化钠

C．用食盐水检验硬水和软水

D．扇闻气体的气味