For two data sets, each of size 5, the variances are given to be 4 and 5 and the corresponding means are given to be 2 and 4, respectively. The variance of the combined data set is

Question

( A ) $\frac{13}{2}$
( B ) $\frac{11}{2}$
( C ) $6$
( D ) $\frac{5}{2}$