問題詳情

30 If you use a gas-fueled water heater, you must keep doors and windows open to improve______ and preventCO poisoning.
(A)variation
(B)ventilation 
(C)vaccination 
(D)verification 

參考答案

答案：B
難度：非常簡單1
統計：A(0),B(1),C(0),D(0),E(0)