The correct option is C It can be the site of energy generation.
Endoplasmic reticulum (ER) exists as a membranous network enclosing a fluid-filled lumen which almost fills up the intracellular cavity. The network of the endoplasmic reticulum is present all over the cell. The endoplasmic reticulum is connected to the nuclear envelope. So, it behaves as transport channel for proteins between nucleus and cytoplasm. The ER facilities transport of materials from one part of the cell to another, thus forming the cell's circulatory system. Mitochondria is the site of energy generation. It is not generated in the endoplasmic reticulum.
So, the correct answer is option C.