They are all close around one half.  Check the numerators to see how
close they are to half the denominator.

a)100/199 <--the numerator is MORE THAN half the denominator
b)1/2     <--the numerator is EXACTLY half the denominator
c)49/99   <--the numerator is LESS THAN half the denominator
d)98/197  <--the numerator is LESS THAN half the denominator

So the answer is a).

Edwin