请判断以下句子正误。如有错误请改正。
1 Some problems of transition might prove more intractable and complexthanappearedat first.
2 The difficulties are even greater than appears at first sight.
3 They arrived earlier than it had been expected.
4The question is more complicated thanappearson the surface
看来，曹老师这次要较真了。好的，我先回答你的这类问题。我觉得这类句子都是错的。
1. Some problems of transition might prove more intractable and complexthanappearedat first. （误）
改正：Some problems of transition might prove more intractable and complexthanthey appearat first.
【说明】本句有两处错误：1. appeared缺少主语；2. appear应改为一般目前时，不需要一般过去时。加了主语后，than充当了appear的表语。
2. The difficulties are even greater than appears at first sight.（误）
改正：The difficulties are even greater than they appear at first sight.
【说明】本句有两处错误：1. appears 缺少主语；2. 由于主语用they，所以把appears 改为复数形式appear。加了主语后，than充当了appear的表语。
【补充】appear 最好改为过去时appeared。假如单纯谈论事实，不改也可。
3. They arrived earlier than it had been expected.（误）
改正：
（1）They arrived earlier than had been expected.
（2）They arrived earlier than expected.
（3）They arrived earlier than people had expected.
【说明】than 在从句中作主语，指代整个主句内容，本句不缺主语，去掉it。than 担任主语时，谓语部分是完整的；反过来讲就是，当谓语部分完整时，than 要担任主语。
句1是完整的被动句；句2是句1的省略句；句3是主动句，添加了主语peole，也可用we等，这个时候，than作了expected的宾语。
4.The question is more complicated thanappearson the surface. （误）
改正：The question is more complicated thanit appearson the surface.
【说明】appears缺少主语。加了主语it后，than充当了appears的表语。
【个人看法】关于than 比较句，它是一个很复杂的问题。
1. 大家忽视than 的固定说法和固定搭配，不予考虑。如：more than five，less than two，no less than, not less than, no more than, not more than，等等。
2. 大家忽视than 从句中的省略现象，不予考虑。因为跟主句内容重复，than 从句省略完全重复的部分。如：It is colder today than yesterday. Its easier to get there on foot than by car.
3. 依据删繁就简的原则，除去上述例外状况，正宗的than 比较结构应该是：
than 除去表示“比...更...”的词语意义以外，它在其引导的从句中需要充当某种成分，或者说它暗示着担任某种成分。这种成分可能是“主语，宾语，表语，状语”（事实上，than充当表语或状语的时候居多，由于比较的多为表语或状语成分），也就是说，在than 从句中一直缺少着某种成分，而缺失的这种成分，被than 义无反顾地担任了。但，than 只能担任其中一种成分，不可以同时担任两种或以上。
4.鉴于此，句1，句2，句4 的错误在于：系动词appear 之后缺少表语，应由than 来充当。既然这样，than 就不可以再担任主语了，所以，这3句都缺少主语。大家依据主句的主语，使用适合的代词加入。
句3 的错误在于：本句不缺主语，应去掉it。由于，当than 从句的谓语部分完整时，than 要在从句中做主语，本句中，than 指代整个主句内容。
关于than 充当从句主语的例句：
This course turned out to be more drastic than was expected.
这疗法的结果比预想的厉害得多。
The price was substantially higher than had been expected.
价格比预计的要高不少。
The changed outlook entails higher economic growth than was previously assumed.
观念的改变必然会使得经济增长高于之前预计的水平。
He never says more than is necessary.
他从不多说没必要的话。（他从不说废话）
He often eats more than is good for his health.
他常常吃的饭量多于对身体有益的量。
Always do more than is required of you.
任何事永远要超需要完成。
He offered more information than is needed.
他提供了多余的信息。
我的第3条看法是重点，也是判断上述句子错误的主要依据。不当之处，请曹老师、各位专家老师和网友指正。
