#### Answer

a) Infinite
b) Finite
c) Empty

#### Work Step by Step

a) The number of counting numbers is infinite. Counting numbers are any positive whole numbers. There are an infinite number of positive whole numbers.
b) The number of vowels is finite. There are only 26 total English letters, so the number of vowels is a finite number.
c) This set is empty, for there is no intersection if two sets are disjoint.