Question

the olmec people
constructed giant stone monuments.
built pyramids out of blocks of stone.
developed a writing system with pictographs.
created a system of numbers that included zero.

Explanation:

The Olmec are known for their iconic giant stone heads and other large stone monuments. Stone pyramids are more associated with later Mesoamerican groups like the Maya and Aztec. A pictograph writing system and a number system with zero were developed by the Maya civilization, not the Olmec.

Answer:

constructed giant stone monuments.