The correct option is A 64
Every generation of a family tree has double the number of members in the previous generation.
Starting from the current generation (1 member),
First generation =1×2=2 members
Second generation =2×2=4 members
Third generation =4×2=8 members
Fourth generation =8×2=16 members
Fifth generation =16×2=32 members
Sixth generation =32×2=64 members