Cardiac muscle cannot be tetanized because of :

a. the presence of high intercellular Ca ions

b. the presence of high K ions

c. cardiac muscle is absolutely refractory

during part of cardiac cycle

d. cardiac muscle is absolutely refractory

during most of cardiac cycle

the syncitial function of the heart depends on the presence of :

a. gap junctions and intercalated discs

b. light and dark filaments

c. Z-lines

d. actin and tropomyosin

see the comments to know the right answer