2. be + 带to的不定式的用法:

带to的不定式可用作be的补足语：
Your mistake was to write that letter.你的错误是写了那封信。
动词do后面也可以跟be+to（可有可无），如：
What you do is (to) mix the eggs with flour.你要做的事是把面粉和鸡蛋搅合在一起。
带to的不定式可以形式上是主动的而意义上却是被动的：
This house is to let/to be let.此房出租。
Who is to blame/to be blamed?该怪谁？
但有些不定式则只能是被动的：
He's (only) to be admired/envied/pitied.他（真）值得尊敬/羡慕/同情。
All this is to be sold.所有这些都是出售的。

3. although和though的区别

although和though在许多情况下用法相同，但是前者在语气上比后者稍强，因此although更常见于句首。
Although/Though he hurried, the train left when he got there.虽然他紧着赶，他到达那里的时候火车还是开走了。
在下面这些情况只能用though,而不能用although.
(1) though可以和even, as连用，构成even though (即使)，as though (似乎)，但不能说even although或as although.
He acted as though he had never heard the news befor.他表现得好像以前从未听过这消息。
(2) though可用作副词，放在句尾，表示"不过"的意思；但although始终只能用作连词。
It was a quiet party. I had a good time, though.这次聚会非常安静，不过，我还是玩得很痛快。
(3) though 还可以用于和特殊句型：形容词/副词+though+主语+动词。
Cold though it was , I went out.尽管天气冷，我还是出去了。