According to the procedure call standard for ARM architecture, the arguments are passed in core registers $($R$0-$R$3)$ and on the stack. When calling a function ${\displaystyle \underset{?}{\overset{?}{}}}(1,2,3,4),$ what is the value of the register R$2?$ Assuming each integer has $32$ bits.

a$.1$

b$.2$

c$.3$

d$.4$