如果（引导条件从句） if
如果你努力学习，你会及格的。 You can pass the exam if you study hard
though ， although ：虽然（引导让步状语从句）和原因状语从句一样，如果用了 though ， although （虽然）就不能再用 but （但是）。
虽然我住在海边，可是我游泳并不好。 Although I live near the sea ， I'm not a good swimmer
Though I live near the sea ， I'm not a good swimmer
I live near the sea ， but I'm not a good swimmer
注意时态一致，和时间状语从句一样。主句是将来时之时，从句要用一般现在时。
太 以致 so that
他太老了，不能工作。 He is so old that he can't work
He is too old to work
箱子太沉了，我抬不起来。 The box is so heavy that I can't lift it
The box is too heavy for me to lift
这个小女孩太漂亮了，每个人都喜欢她。 The girl is so beautiful that everybody likes her
so that 在肯定句中不能转换成 too to 。
并列结构中， or 通常用于否定句， and 用于肯定句。
在月球上没有空气和水 There is no air or water on the moon
There is no air and no water on the moon
在否定中并列结构用 or 连接，但含有两个否定词的句子实际被看作是肯定结构，因此要用 and 。
我不喜欢鸡和鱼， I don't like chicken or fish
我不喜欢鸡，但我非常喜欢鱼 I don't like chicken but I like fish very much
否定句中表并列用 or， but 表转折。
没有水和空气 我们会死 We will die without air or water
We can't live without air and water
否则。 or
我必须努力，否则我通不过考试 I must work hard or I'll fail in the exam
either or意思为"或者 或者 "。注意谓语动词采用就近原则。
或者你对，或者我对 Either you or I am right
他们坐下来 谈论一些事情。 They sat down and talked about something
他们开始跳舞和唱歌。 They started to dance and sing
我看见两个人坐在后面 窃窃私语。 I saw two men sitting behind and whispering there
and 还可以和祈使句或名词词组连用表示条件。（ or 也有此用法）
下定你的决心 你就会有机会。 Make up your mind and you'll get the chance
If you make up your mind you'll get the chance
再多的努力一次 你会成功的。 One more effort and you'll succeed
If you make one more effort you'll succeed
but 表示转折， while 表示对比。
一些人喜欢猫，而另一些人讨厌它们 Some people love cats while others hate them
今晚你想回来吃晚餐吗？我想，但是我太忙 Would you like to come to dinner tonight ? I'd like to, but I'm too busy
他摔伤了他的腿 所以他不能玩游戏。 He hurt his leg so he couldn't play in the game
两个并列连词不能连用，但 therefore ,then, yet 可以和并列连词连用。
你可以看电视，或者你可以去睡觉。 You can watch TV or you can go to bed
他摔伤了他的腿 所以他不能玩游戏。 He hurt his leg and so he couldn't play in the game
He hurt his leg and therefore he couldn't play in the game
although yet ，但 although 不与 but 连用。
虽然他很虚弱 但他尽其所能做这项工作。 Although he was weak yet he tried his best to do the work