Based on the Ontario Building Code, Consider Division B$,$ Table $9\mathrm{.}15\mathrm{.}4\mathrm{.}2.$A$,$ Sentence $9\mathrm{.}15\mathrm{.}4\mathrm{.}2.(1)$ and the following sketch. $20$MPa

plain concrete is to be used for a basement wall. What is the minimum wall thickness required to support the backfill?

a$.150mm$

b$.240mm$

c$.200mm$

d$.140mm$