Explanation

(d)
The series of binomial coefficient is
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^{15}C_{8}$
$\overset{\ ^{15}C_{0},^{15}C_{1},^{15}C_{2}\ ,\ldots,^{15}C_{7}\ }{\overset{\leftarrow}{decreasing\ value}}$ $\downarrow$ $\underset{decreasing\ value}{\overset{\ ^{15}C_{9},\ldots,^{15}C_{9},^{15}C_{15}}{\rightarrow}}$
From the above discussion, we can say that decreasing series is $\ ^{15}C_{7},\ \ ^{15}C_{6},\ \ ^{15}C_{5}$.