For example, when someone says "how are you", which one is better to answer?
I'm fine. What about you?
I'm fine. How about you?
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Sign up to join this communityFor example, when someone says "how are you", which one is better to answer?
I'm fine. What about you?
I'm fine. How about you?
Hello, how are you?
is usually an example of phatic language, which are ROUTINE expressions intended to open friendly communications rather than intended to impart or elicit information. (In some contexts, for example when your doctor visits you in the intensive care unit of a hospital, it is both phatic and substantive.)
When the intent is just phatic, it is usually best to respond with equally phatic language. Person A signals to person B "I'm friendly," so person B signals back "I'm friendly too."
The phrase "Thank you" or "thanks" needs to be in the response. Your health and well being have been inquired about to show concern for you. You express gratitude for that concern with thanks. And then you show reciprocal concern for your greeter.
The rest of the response is a bit more free form.
Fine, thanks, and you?
Not bad, thank you. And how are you?
Great, thank you. What about you?
All those work. Notice that all the answers respond briefly to the substance of the question; it is not ignored. They all express thanks for the concern shown. They all show reciprocity. This is about manners, not grammar. Personally, I'd probably not use "what" because I'd prefer not to introduce something non-parallel into what is meant to be understood without conscious thought, but there is nothing inappropriate in "what."