板式换热器的进、出口严禁安装（）。
A、闸板阀
B、减温阀
C、节流阀
D、球阀
参考答案：D
穗状轮伞花序顶生的药材为
A．金钱草B．鱼腥草C．茵陈蒿D．荆芥E．薄荷
Because she enjoys the life in the city, Nancy_____ goes to the countryside.
A. often
B. usually
C. always
D. hardly ever
