Q: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Question: The system in T:
Options: <1> It is present in all muscle cells without exception. <2> It is part of the sarcoplasmic reticulum. <3> It has an ATPase activated by Ca2 +. <4> It is a tubular invagination of the plasma membrane. <5> Releases Ca2 + to the cytosol during recruitment.
A:
4