I think it important to learn English well.
请问这种句子是什么结构？ it 后面为何不需要is?
I think it important to learn English well.
请问这种句子是什么结构？ it 后面为何不需要is?
【答】这是复合宾语结构：think + 宾语 + adj. （形容词作宾补）。
你问“it 后面为何不需要is?” 其实，加is也可以，但结构变为：think + that ...（宾语从句）
I think （that）it is important to learn English well.
相对而言，用复合宾语结构，看上去简练，由于它是个简单句。而加了is 后，成了复合句，结构变得复杂一些。
下面，我重点讲讲：英语的“6123结构”的意思是？
在新课标人教版必学四第3单元中，有如此一个句子：You may find it astonishing that Charlie was taught to sing as soon as he could speak and dance as soon as he could walk. 句子意思是：“你或许会感到惊奇，在查理刚能说话时大人就教他唱歌，他刚能走路时大人就教他跳舞。”
本句含有一个容易见到的句型结构：find + it + adj. + that从句。句中的it作形式宾语，真的的宾语为that从句（其中that从句又包括一个由as soon as 引导的时间状语从句），astonishing 为形容词作宾语补足语。真的的宾语也可以由不定时或动名词充当。比如：
We found it quite pleasant to work with him. 大家发现跟他一块工作非常愉快。
I felt it hard to communicate with them. 我感觉很难跟他们交流。
He considers it quite foolish to do like that. 他觉得那样做非常愚蠢。
We think it no use complaining. 大家觉得抱怨是没用的。
该句式中的it作形式宾语。为了记忆便捷，大家称该句型为“6123结构”。
【说明】这种称谓只是为了学习和记忆，而且，这类动词是英语学习中最容易见到的，不肯定包揽所有状况。
“6”指主句中6个常用动词：think,consider, believe,make,find, feel。“1”指形式宾语it；“2”指宾补的两种形式：形容词或名词；“3”指真的宾语的三种形式：①不定式短语，②动名词短语，③that引导的宾语从句。
This special strain of rice makes it possible to produce one-third more of the crop in the same fields. 这种特殊的稻种可以在同样的田里增加三分之一的农作物产量。（必学四第2单元）
This produced a chain reaction, which made it possible for life to develop. 这产生了连锁反应，使得生命孕育进步成为可能。（必学三第4单元）
He didn’t make it clear when and where the meeting would be held. 大家还没有弄了解会议将在何时何地召开。
She made it a rule to get up at six and take a walk in the morning. 她在早晨六点起床然后散步已成为习惯。
Do you find it funny to see someone sliding on a banana skin? 看见有人踩在香蕉皮上滑倒，你感觉有趣吗？
The teacher feels it his duty to help the student with his English. 老师感到，帮助学生学英语是我们的责任。
We thought it necessary that the two sides should sTOP arguing. 大家觉得，双方停止争论是必要的。
I consider it rude to stare at other people. 我觉得，双眼盯着其他人看是无礼的。
We believe it useless reading without understanding. 大家觉得，不理解的状况下阅读是没用的。
He considered it a good thing that the parliaments would be involved. 他觉得，议会将卷入其中是好事一桩。
Ann felt it an justice that she had been automatically blamed. 安感觉，她已自动同意职责是公正的。
They find it a mystery that he has never mentioned his parents. 他从来没提到过我们的爸爸妈妈，他们发觉真是个谜团。
We consider it necessary that the machine should be oiled regularly. 大家觉得，有必要对这台机器常常加油润滑。
Under the circumstances I feel it right that you should know. 在这样的情况下，我感觉你应该了解。
I found it strange that she had not come yet. 她居然没来，我发现奇怪。
Mr. Black made it clear that the students should prepare every lesson. 布莱克先生明确指出，学生应筹备每一节课。
I think it important that we should keep calm. 我觉得大家维持冷静是非常重要的。
I find it difficult to do the job well. 我发现做好这件事困难。
I consider it best that you should stay here. 我觉得你最好住这儿。
I find it easy to get on with her. 我发现她比较容易相处。
They haven’t made it known where they are to hold the conference. 他们还没有宣布会议在哪儿开。
【特不要说明】上述6个动词中，除去make 以外，其他5个动词think,consider, believe, find, feel，都可以接两种结构：
1. think：
think + 宾语 + 宾补（形容词或名词充当）
think + that...
2. consider
consider + 宾语 +宾补（形容词或名词充当）
consider +that...
3. believe
believe + 宾语 +宾补（形容词或名词充当）
believe +that...
4. find
find + 宾语 +宾补（形容词或名词充当）
find +that...
5. feel
feel + 宾语 +宾补（形容词或名词充当）
feel +that...
