There are many expressions commonly used in English with the comparison form ‘as … as’.
There is no magic rule to help you remember them. You just have to learn them. Sorry!
Take a look at the examples below.
As good as gold.
This expression if often (but not only) used to describe children who are very well behaved.
E.g. The children played happily all day. They were as good as gold and there was no stress for anyone.
As blind as a bat.
If someone is as blind as a bat they have poor eyesight and cannot see very well.
E.g. Without his glasses he’s as blind as a bat!
As clean as a whistle.
If something is as clean as a whistle it means it is extremely clean.
E.g. She spent all afternoon cleaning and polishing her car. She did a great job – it’s as clean as a whistle.
Have fun learning English!
Louise