its / it's

　　its: possessive determiner similar to 'my' or 'your'

　　its：物主代词，和“我的”或者“你的”是一类的。

　　Examples:

　　例句：

　　Its color is red.

　　The dog didn't eat all of its food.

　　它的颜色是红色。

　　这只狗没有把它所有的事物吃掉。

　　it's: Short form of 'it is' or 'it has'

　　it's：it's是it is或者it has的缩写。

　　Examples:

　　例句：

　　(it is) It's difficult to understand him.

　　(it has) It's been a long time since I had a beer.

　　(it is)要理解他太困难了。

　　(it has)我很久没喝过啤酒了。