空调设备关闭后再重新启动时,应间隔()以上。
A.4min
B.5min
C.6min
D.3min
参考答案:D
下列选项中,对于指定项目的数目前后相等的是 ( )
A.电子数:17gOH—与1mol-OH
B.双键数目:1mol与4mol C2H4
C.分子数:常温常压下16g氧气与4g氦气
D.阴离子总数:72gCaO2与62g Na2O
_________ we had making snowmen last Sunday![ ]
A. What a great fun
B. What great fun
C. How a great fun
D. How great fun