当产品市场上国民收入处于均衡状态时,计划存货投资和非计划存货投资都为零。
参考答案:错
— What a clean and bright classroom, isn't it?
— Yes, it's always clean and bright because it _____every day.
A. cleans
B. cleaned
C. is cleaned
D. was cleaned
下列实验操作或原理不正确的是 ( )
A.蒸馏操作时,温度计水银球的位置应在蒸馏烧瓶的支管口处
B.分液操作时,分液漏斗中的下层液体从下口放出,上层液体从上口倒出
C.萃取操作时,应选择有机萃取剂,且萃取剂的密度必须比水大
D.测定溶液pH的操作:将pH试纸置于表面皿上,用玻璃棒蘸取溶液,点在pH试纸的中部,与对应的标准比色卡比较