The answer is B: purple star.

The rule
The pattern repeats every 3 things: purple star, purple star, purple square. Then it starts again from the beginning.
The pattern as Python code
Here is a tiny Python program that follows the same rule. Type it into IDLE and run it to print the whole pattern, including the answer.
pattern = ["purple star", "purple star", "purple square"]
for position in range(8):
print(position + 1, pattern[position % len(pattern)])
When you run it, Python prints:
1 purple star 2 purple star 3 purple square 4 purple star 5 purple star 6 purple square 7 purple star 8 purple star
Pixel says: Try changing a number in the code and run it again. Can you make the pattern go on for 20 steps? Meow!