How many main types of muscles are there?

The term $refractory$ $period$ with reference to muscle tissue refers to:

Sarcolemma is the covering of

Identify the odd one out from the following list.

$A$: Application of stimuli repeatedly just at the start of relaxation of a muscle fibre shows an increase in the extent of contraction initially and results in treppe or staircase phenomenon.
$R$: It can be attributed to the summation effect of the sub-threshold stimuli being given again and again.

In a muscle fiber,$Ca^{++}$ is stored in the .....