#### Answer

a.) continuous
b.) discrete
c.) continuous
d.) discrete

#### Work Step by Step

A discrete variable is a variable that can only take on a finite number of values in an interval. For example the number of people can only be an integer; 2.7 people make no sense.
On the other hand, continuous variables can take on infinite number of values. A weight of a dog can be infinitely precise, with infinitely many decimal places, just like the length of time to run a marathon.