Meaning of gather

[Veki]

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

Your answer was: n/a
_________________________

PLease, answer me.
I don't see a reason why I can't use "collected" or "assembled" like a right answer.
I don't see some big differnece between "gathered", "collected" and "assembled"?

Another question I don't understand a meaning of "keen on flying" ("keen" can have so lot of meaning!)

Thank you a lot

[Rich7]

In this case "gather" means to notice. that's why, this, is the correct answer.

[Torsten]