Answer
From largest to smallest: $ A,C,B~and~D $.
Work Step by Step
For the first lens A:
We know that $ D=\frac{f}{f-number}$
We plug in the known values to obtain:
$ D=\frac{150mm}{1.2}$
$ D=125mm $
For the second lens B:
$ D=\frac{f}{f-number}$
$ D=\frac{150mm}{5.6}$
$ D=27mm $
For the third lens C:
$ D=\frac{35mm}{1.2}$
$ D=29mm $
For the fourth lens D:
$ D=\frac{35mm}{5.6}$
$ D=6mm $
Now we rank the lenses in order of decreasing aperture size as $A,C,B~and~D $.
