The answer is C: pink heart.

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