Meaning of "keen on"

[nana]

Test No. incompl/inter-30 "Flying on a Plane", question 9

As you've probably ........., I'm not really keen on flying.

(a) collected
(b) gathered
(c) assembled
(d) accumulated

Test No. incompl/inter-30 "Flying on a Plane", answer 9

As you've probably gathered, I'm not really keen on flying.

Correct answer: (b) gathered
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hello,

please help me:

"keen on" is the idiom or just a word?
it's meaning is changed depend on the context, isn't it?

Thanks very much.

[Alan]

Hi Nana,

Keen on means that you like someone or something or you have a liking for as used in the following: She's very keen on him - she likes him very much. He's very keen on all types of sports - he likes to watch/take part in sport.

Alan
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English as a Second Language
You can read my ESL story Present Simple

[Irshkur]

Keen on is also when you are a big FAN of something, but I think it's more of a British way of speaking?