A data set consist of a set of numerical values. Which if any of the following statements could be correct?

a. There is no mode.
b. There are two modes.
c. There are three modes.

c is correct, but what about a and b? are they possible as well?

What is a mode? Here are some examples:
http://www.mathsisfun.com/mode.html
http://www.purplemath.com/modules/meanmode.htm