The answer is A: green heart.

The rule
The pattern repeats every 4 things: purple square, green heart, blue circle, green heart. 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", "green heart", "blue circle", "green heart"]
for position in range(10):
print(position + 1, pattern[position % len(pattern)])
When you run it, Python prints:
1 purple square 2 green heart 3 blue circle 4 green heart 5 purple square 6 green heart 7 blue circle 8 green heart 9 purple square 10 green heart
Pixel says: Try changing a number in the code and run it again. Can you make the pattern go on for 20 steps? Meow!