The answer is C: pink diamond.

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