# 20. Consider the following block diagram in th...

20. Consider the following block diagram in the figure.

The transfer function $C(s)\over R(s)$ is

(A) $G_1G_2\over {1+G_1G_2}$

(B) G1G2+G1+1

(C) G1G2+G2+1

(D) $G_1\over1+G_1G_2$

Hint: