问题
选择题
A giant helium(氦) balloon is telling residents of Paris how good or bad the air quality is. When it’s good, the balloon ----measuring 22 meters wide and 32 meters high---shines green. _________, it’s red.
A．Though terrible
B．Whenever good
C．If worse
D．When bad
答案
答案：D
考查状语从句的省略。根据句子，可知前后是对比相反情况，所以前面是When it’s good,，后面应是When it is bad,it is 可以省略，所以选D。