What is the overall transfer function (C/R) of the following block diagram if G = G1. G2. G3 and H = H1.H2 ?

What is the overall transfer function (C/R) of the following block diagram if G = G1. G2. G3 and H = H1.H2 ?

A. 1/(1 + GH)
B. G/(1 + GH)
C. H/(1 + GH)
D. G/(1 – GH)