The answer is A: teal triangle.

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