1. My sister eats like a bird.
我妹妹饭量很小。
还能这样说：
My sister eats very little.
My sister doesn't eat very much.
谚语：
A bird in the hand is worth two in the bush.
一鸟在手胜于两手在林。（到手的东西才是可靠的。）
2. My old brother eats like a horse.
我哥哥特别能吃。
还能这样说：
My old brother eats very much.
My old brother is a big eater.
谚语：
A short hurse is soon curried.
矮马容易刷洗；小事易办。
3. I'm full!
我饱了！
还能这样说：
I feel stuffed.
I am quite enough.
应用解析：
full size 原尺寸；
in full bloom 盛开的；
to the full 充分地，尽情地；
4. Hamburger is my cup of tea.
我喜欢吃汉堡。
还能这样说：
I like to eat hamburger.
I love hamburger.
谚语：
An unfortunat man would be drowned in a tea-cup.
人若倒霉，一杯茶也能淹死。