The answer is C: pink circle.

The rule
The pattern repeats every 2 things: purple square, pink circle. 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 square", "pink circle"]
for position in range(8):
print(position + 1, pattern[position % len(pattern)])
When you run it, Python prints:
1 purple square 2 pink circle 3 purple square 4 pink circle 5 purple square 6 pink circle 7 purple square 8 pink circle
Pixel says: Try changing a number in the code and run it again. Can you make the pattern go on for 20 steps? Meow!