The correct option is A nucleus
∙ Nucleus is a small spherical mass located in the cytoplasm which regulates and controls all cell activities.
∙ Vacuoles are the storage sacs of the cell. They store water, salt, excretory materials.
∙ Plastids are of three types depending on the pigment they contain and the color they impart to plant parts (chloroplast, chromoplast, leucoplast).
∙Cytoplasm is a semifluid, colorless and translucent substance found between the nuclear membrane and cell membrane.