The answer is C: red heart.

The rule
The pattern repeats every 4 things: red heart, red heart, pink heart, 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 = ["red heart", "red heart", "pink heart", "green heart"]
for position in range(10):
print(position + 1, pattern[position % len(pattern)])
When you run it, Python prints:
1 red heart 2 red heart 3 pink heart 4 green heart 5 red heart 6 red heart 7 pink heart 8 green heart 9 red heart 10 red 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!