Say for $T(4,2)=T(2^{2},2^{1})$ answer should be $\binom{2+1}{1}=3$
Now try with recursion tree
$T(4,2)=T(2,2)+T\left ( 4,1 \right )$
$T(2,2)=T(2,1)+T\left ( 1,2 \right )=1+1=2$
So, $T(4,2)=T(2,2)+T\left ( 4,1 \right )=2+1=3$
Answer Matched
Take another one $T(8,4)=T(2^{3},2^{2})$
So, according to option answer should be $\binom{3+2}{2}=10$
Now try with recurrence tree
$T\left ( 8,4 \right )=T\left ( 4,4 \right )+T\left ( 8,2 \right )$
$T\left ( 4,4 \right )=T\left ( 4,2 \right )+T\left ( 2,4 \right )$
$T\left ( 4,2 \right )=T\left ( 2,2 \right )+T\left ( 4,1 \right )$
$=T\left ( 2,1 \right )+T\left ( 1,2 \right )+T\left ( 4,1 \right )=3$
$T\left ( 2,4 \right )=T\left ( 2,2 \right )+T\left ( 1,4 \right )=T\left ( 2,1 \right )+T\left ( 1,2 \right )+T\left ( 1,4 \right )=3$
$T\left ( 8,2 \right )=T\left ( 4,2 \right )+T\left ( 8,1\right )=3+1=4$
Then, $T\left ( 8,4 \right )=T\left ( 4,4 \right )+T\left ( 8,2 \right )=6+4=10$
Again it is matched with option
Ans $D)$