Smooth er of a muscle cell:
a. sarcomere
b. sarcoplasmic reticulum
c. arcolemma
d. sarcoplasm

B. Sarcoplasmic reticulum

Explanation: The sarcoplasmic reticulum is the name given to the organelle in the muscle cell, in charge of the storage and regulation of the intracellular calcium levels. It is the smooth endoplasmic reticulum in muscle cells, it means that it does not have ribosomes in its surface.

Option A. Incorrect. A SARCOMERE is the functional and anatomic unit of the striated muscle (skeletal muscle and heart muscle). This word comes from the greek: sarkos (meat), meros (part). That is reason you could find other structures of the muscle cell with this root (SARCO...).

Option C. Incorrect. "Arcolemma" this word does not exist. But if it refers to SARCOLEMMA, this word means: sarko (meat), lema (cortex) in greek. It is the plasma membrane of the muscle cells.

Option D. Incorrect. The SARCOPLASM, comes from the greek: sarko (meat), plasm (matter). This structure is the citoplasm of the muscle cells.

In conclusion, the word SARCOPLASMIC RETICULUM, refers to a structure of the muscle cell, that in this case, is the RETICULUM or the SMOOTH ER.

answer: the answer is d.

explanation: this is because when you exercise you make your muscle produce a certain liquid, that does not evaporate it.   also when you exercise you do not reduce muscle fiber.   and it does not really control your twitch that much.