Zebadiah has 3 red shirts,3 blue shirts, and 3 green shirts in a drawer. Without looking, he randomly pulls shirts from his drawer one at a time. He would like a set of shirts that includes either 3 of the same colour or 3 of different colours. What is the minimum number of shirts that Zebadiah has to pull out to guarantee that he has such a set?
Answer Choices
A. 4
B. 3
C. 6
D. 5
E. 7