Question

select the part whose main job is to direct cell activities by sending instructions to different parts of the cell. centrosome ribosome mitochondria nucleus

Explanation:

The nucleus contains the cell's genetic material (DNA). DNA holds the instructions for making proteins and directing all cell activities. The centrosome is involved in cell division (organizing microtubules). Ribosomes are for protein synthesis (using mRNA instructions from the nucleus). Mitochondria are the power - houses (produce ATP). So the nucleus is the control center directing cell activities.

Answer:

nucleus