1.There (D) a dirty river here,but now it has become quite c

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1.There (D) a dirty river here,but now it has become quite clean.
A.would be B.ought to be C.has been D.used to be
【为什么不选A?】
2.What he said has us (A) all night.
A.laughing B.to laugh C.laugh D.laughed
【为什么不选C?】
关于第一题，我们语法解释那里有说【would 还可表示过去的习惯性动作，意为“常常，总是”，相当于used to】

1 从句意上说,become说明a dirty river 是以前的实际情况,所以用过去时
你说的A,过去将来时,表示你过去期望它现在脏,就不存在后面的become了
所以不符合提议
针对你的补充
Used to可指过去的状态或情况,would则不能,would强调反复发生的动作
2 这里的have是使役动词,have sb do/doing都可以
后面的all night说明laugh是持续的所以用laughing

1.There (D) a dirty river here,but now it has become quite c There ___ a river in front of the house but now it has turne “___a river near here?” A.Are there B.There is C.There are D The river has become very dirty和the river has been very dirt There --- a dirty lake, now here is a beautiful garden. A us but I enjoy it ------- A quite B much too C very D very much it's（）useful book a.quite b.a quite c.quite an d.an quite there was a beautiful castle in the city,but now it has disa There____low and dirty houses here,but _____you can see now 1、Alll but one__here just now(A.is B.was C.has been D.were) There is little water here; but there are quite a few empty He is new here,but he has quite a lot of friends________.