Final answer:
The number of ways of selecting 10 balls out of an unlimited number of white, red, blue, and green balls is 4^10.
Step-by-step explanation:
The number of ways of selecting 10 balls out of an unlimited number of white, red, blue, and green balls can be calculated using the concept of combinations. Since each ball can be one of the four colors, there are 4 choices for each of the 10 balls. Therefore, the total number of ways is 4^10, which is option a.