D) is answer
Given that
$x1+x2+x3=11$ where, $x1\geqslant 1,x2\geqslant 2,x3\geqslant 3$
Let $x1=x1{}'+1, x2=x2{}'+2, x3=x3{}'+3$
Using above equation we can write $x1{}'+1+x2{}'+2+x3{}'+3=11 \Rightarrow x1{}'+x2{}'+x3{}'=5$
Now it is the case of combination with repition which is given by $\binom{n+r-1}{r}$
so Answer is $\binom{3+5-1}{5}=\binom{7}{5}=\binom{7}{2}$