'member of the gym' vs 'member by the gym'

[Ummy]

Business English Courses, Elementary Level

ESL/EFL Test #42 "Basic Business English", question 5

She is a member ......... the gym.

(a) for
(b) from
(c) by
(d) of

Business English Courses, Elementary Level

ESL/EFL Test #42 "Basic Business English", answer 5

She is a member of the gym.

Correct answer: (d) of

Your answer was: incorrect
She is a member by the gym.
_________________________

why of and not by?

Ummy

[Mister Micawber]

.
We are members 'of' organizations, not 'by' organizations, Ummy.
.
_________________
Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mr. Micawber