For the differential amplifier, vG$1=0\mathrm{.}9$ V $+0\mathrm{.}1$ V sin$($t$)$ and vG$2=0\mathrm{.}9$ V $-0\mathrm{.}1$ V sin$($t$).$ The common$-$mode voltage is

Group of answer choices

$0\mathrm{.}9$ V

$1\mathrm{.}0$ V

$0\mathrm{.}8$ V

$0\mathrm{.}1$ V sin$($t$)$

$-0\mathrm{.}1$ V sin$($t$)$

$0\mathrm{.}2$ V sin$($t$)$

$-0\mathrm{.}2$ V sin$($t$)$