The answer is D: green hexagon.

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