Answer is (D).
$G_1$ results in strings $b, ab, bb, aab, abb, bbb,$ ... i.e $a^mb^n$, $m\geq 0$ and $n > 0$ (and because only $a$'s are not possible but only $b$'s are)
$G_2$ result in strings $a, b, aa, ab, bb, aaa, aab, abb, bbb$ ... i.e $a^mb^n$, $m > 0$ or $n > 0$ (or because only $b$'s is possible $b,bb,bbb,$ , only $a$'s are possible)