$A$ motor unit is a

Which ions must be present for the binding of cross-bridges during muscle contraction?

Where are calcium ions stored in muscle cells?

Given below are two statements:
$Statement-I$: Plasma creatinine is produced during catabolism of creatinine phosphate in skeletal muscle contraction.
$Statement-II$: Creatinine phosphate provides a ready source of high-energy phosphate.
In the light of the above two statements, choose the most appropriate answer from the options given below.

Match the following components with their respective locations and functions:
$(1)$ Synovial fluid
$(2)$ Troponin

Which of the following statements regarding the types of muscles present in our body is correct?