I've dropped my car key! What do you think are the keys to success?
Which 'key' is abstract (an idea)? Which 'key' is concrete (a thing)?
It is important to know the difference between words that are about
ideas (ABSTRACT)
things you can touch, hold or count (CONCRETE)
because this affects your grammar.
In the picture below, 'key' is a CONCRETE noun - it is something you can touch, see and hold. It is something you use to open a door, and you can have many keys.
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In the next picture, a job interview is happening and the person might be asked:-
"What do you think are the keys to success?"
'keys' is an ABSTRACT noun. The 'keys' to success are not things you can see and touch and hold. No, they are simply ideas to help you become successful.
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