Idiom: not have a leg to stand on

[Toma]

Business Idiom in English, Intermediate level

ESL/EFL Test #138 "Ways of disagreeing", question 10

You might as well admit it! You haven't a ......... to stand on.

(a) foot
(b) arm
(c) hand
(d) leg

Business Idiom in English, Intermediate level

ESL/EFL Test #138 "Ways of disagreeing", answer 10

You might as well admit it! You haven't a leg to stand on.

Correct answer: (d) leg

Your answer was: incorrect
You might as well admit it! You haven't a foot to stand on.
_________________________

please explain me why it's foot and not leg here.

thanks in advance
Toma

[Conchita]

The standard idiom is: not have a leg to stand on, meaning 'to have no chance of success', 'to have no justification'.