meaning of "on one's side"

[Lotuss]

Business Idiom in English, Intermediate level

ESL/EFL Test #63 "How to agree", question 1

You can be absolutely sure I'm on your ..........

(a) road
(b) corner
(c) route
(d) side

Business Idiom in English, Intermediate level

ESL/EFL Test #63 "How to agree", answer 1

You can be absolutely sure I'm on your side.

Correct answer: (d) side
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i can't understand the question?

Lotuss

[Nanucbe]

in one's(road)way-hindering
in one's corner-one's place
on one's side- support
You can be absolutely sure that I support you. (I'm on your side.)

The last one alone can be the indisputably correct word for completiing such an expression. Even if others argue that other words can also complete, this one is correct and no one can say anything against this.
So this is the answer.
narayanan.