BF 3 、 B 6 H 6 、 Al 2 Cl 6 都是稳定的化合物, BH 3 、 AlCl 3 则相对不稳定,其原因是( )。
A.
前者形成大 П 键,后者缺电子
B.
前者缺电子,后者有多中心键
C.
前者通过大 П 键、多中心键、配位键补偿了缺电子,后者缺电子
D.
前者有配位键,后者缺电子
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参考答案:
举一反三
【单选题】There is a sentence in the second paragraph: 'In a hundred closed cafes the espresso machines give an expiring hiss, as if at last slipping off their shoes and wiggling their toes. ' How do you unders...
A.
It means that the coffee machines have been used for too much and cannot be used any longer.
B.
It implies that the owners of these cafes are so tired that they just want to have a good rest.
C.
It suggests that the owners of these cafes have lost their shoes and their toes feel painful with cold.
D.
The coffee machines are going to stop working; it is just like what a person does before he goes to bed after a day's hard work.