Contrasting: 可是，但是，不过，倒，and 却

可是 (kěshì) / 但是 (dànshì)："but" conjunction 

There are two main words for "but" in Chinese: 可是 (kěshì) and 但是 (dànshì). These are largely the same. The small difference is that 可是 (kěshì) is a bit more formal and more common in northern China, whereas 但是 (dànshì) is more informal and a bit stronger in tone. You really don't need to worry about "which one is the right one to use" though. They can be used interchangeably: Statement, 可是 / 但是 + [contrary statement]

• 中文很难，可是学中文很有意思。Chinese is hard, but learning Chinese is interesting. 

• 我很喜欢这个智能手机，但是它太贵了。I like this smart phone, but it is too expensive. 

• 虽然这个台式机不贵，但是我还是不想买。Although this desktop is inexpensive, I still don't want to buy it.

不过(búguò)： a softer "but"
Instead of just using 可是 or 但是, you can also use the softer and more informal 不过 (búguò). The meaning is closer to "however" or "nevertheless" in English. "不过" is a conjunction that comes between two distinct clauses: Clause 1, 不过 + Clause 2

• 喝酒可以，不过不能太多。It's okay to drink some wine, but drinking too much is not acceptable. 

• 扎克伯格的词汇量很大，不过他的声调不太好。Mr. Zuckerberg has a very large vocabulary, but his tone isn't very good. 

却 (què): "however" adverb 

It is an adverb, usually used to indicate something was contrary to expectations, and it is generally followed by a negative comment: clause 1, Subject + 却 + negative comment. If there is a subject in the second clause, however, 却 definitely need to come after it.

• 我邀请他了，可他却没有来。I have invited him. However, he did not show up.
• 他虽然只有三岁，但他会背的诗却比很多大人会的都多。Even though he's only three, the poems he knows are more than those some adults know. 

• 这家饭店的装修很棒，可是菜的味道却很难吃。The interior decoration of the restaurant looks great. However, the taste of its food isn't good.

倒 (dào) ：expressing contrariness 

倒 can be used to express something is contrary to expectations, acting as a turning point in the sentence. It is generally followed by a positive comment: A + negative comment, B + 倒 + positive comment

• 她的男朋友长得不太好看，但人倒是很好。Her boyfriend doesn't look handsome, but his personality is very good. 

 

• 这个笔记本电脑的外观不怎么好看，可性能倒是不错。The look of this laptop isn't that good, but its performance is satisfactory. 

Please filling the blacks by using 可是，但是，不过，倒，or 却.

1)  他要减肥，_______他睡觉前还想吃冰淇淋。

2）这个笔记本很新，价格_______也不贵，我很想买一台。

3）这种糖好吃是好吃，_______您最好不要吃太多。

4）他减肥减了两个多月了，________体重____一点儿也没有减下来。

5）虽然中国发展很快，________污染越来越严重。

6）这个打印机我上个月刚买的，可它______现在坏了。

7）她很开朗，总是有很多话要说，可她今天_____一句话都没说。

8）他很困，______却睡不着。

9）这件衬衫很好看，_______颜色有点儿深，最好搭配一件浅颜色的外套。

10）Grace："我肚子不饿，______我喜欢吃！"

Reference:
http://resources.allsetlearning.com/chinese/grammar/Main_Page