You Have a Choice Between Two Lenses of Focal Lengths

Multiple Choice

You have a choice between two lenses of focal lengths f_a and f_b,where f_b = 2f_a,to use as the objective lens in building a refracting telescope.If the magnification you obtain using lens a is M_a,what will be the magnification when using lens b?

A) M_b = 2 M_a
B) M_b = 4 M_a
C) M_b = 8 M_a
D) M_b = M_a/4
E) M_b = M_a/2