Two events are independent if the knowledge that 
one has occurred does not make the occurrence of 
the other either more likely or less likely.  

First we'll look at c:

>>...Phone call arrival rates at a university admissions 
office and time of day...<<

The probability of a phone call changes if we are given 
that the time is 6AM. So they are NOT independent.

Now we'll look at b:

>>...Car accident rates and the driver’s gender...<<

The probability of an accident changes if we are given 
that the driver is a young male.  So they are NOT 
independent.


>>...Gender of two consecutive babies born in a hospital...<<

The probability that the second baby is a boy DOES NOT change 
if we are given that the first baby is a girl.  It also does
not change if we are given that the first baby is a boy.

So they ARE independent.  The correct choice is a.

Edwin