$A : Ca^{2+}$ plays an important role in muscle contraction.
$R : Ca^{2+}$ combines with the troponin chain,displacing tropomyosin and allowing the myosin head to combine with actin to form an actomyosin complex.

Consider the following four statements $(a-d)$ and select the option which includes all the incorrect ones:
$(a)$ Skeletal muscle fibre is a syncytium as the sarcoplasm contains many nuclei.
$(b)$ In the centre of each $I$-band is an elastic fibre called $H$-line which bisects it.
$(c)$ In the resting state,a subunit of troponin masks the active binding sites for myosin on the actin filaments.
$(d)$ The contraction of a muscle fibre takes place by the sliding of the thick filaments over the thin filaments.

Which of the following is the contractile protein of a muscle?

Sarcoplasm is the

Muscle is attached to bone by

Give the name of the subunits of Troponin.