有3路公共汽车共用一个总站,1路车5分钟发一次车,2路车4分钟发一次车,4路车3分钟发一次车。如果这3路公共汽车同时出站,至少过( )分钟它们又同时发车。
60
用所给动词的正确形式填空。
(1) — Why isn't Jim here?
— He's busy. He __________ (take) care of his aunt's baby at home now.
(2) — What's Mr. Clarke going to do tomorrow?
— He'll go fishing if it __________ (not rain).
(3) Linda __________ (make) a lot of friends since she came here last autumn.
(4) — Did Jack finish__________ (clean) the house this morning?
— Yes, he did.
(5) — Have you heard of the Great Wall, Mr. Read?
— Yes, I have. It's a place of great interest in China.
It _________ (build) thousands of years ago.
矿井瓦斯等级,根据矿井相对瓦斯涌出量,矿井绝对涌出量和瓦斯涌出形式划分为几类?