Let there be $N$ such hosts.
Then when one host is transmitting then others must be silent for successful transmission.
So the throughput per host
$0.16 = 0.2 \times 0.8^{N-1}$
$\implies 0.8 = 0.8 ^{N-1}$
on comparing the exponents, since base are identical
$N-1=1, N=2.$
Correct Answer: $B$