The correct answer will be option-sarcoplasmic reticulum.
Explanation:
The sarcoplasmic reticulum is the membrane bound endoplasmic reticulum of the muscle cell which stores a large amount of Ca⁺² ions.
The reticulum contains Calsequestrin- a calcium binding protein which binds around 50 Ca⁺² ions to itself and helps store more calcium. These calcium ions are released when the signals through T-tubules are carried to the reticulum which leads to the opening of the calcium channels.
Thus, sarcoplasmic reticulum is the correct answer.
