Question 3
Which pair gives two structural differences between human cardiac muscle fibres and skeletal muscle fibres?
The right answer is the one marked above.
Cardiac fibres are branched and uninucleate; skeletal fibres are unbranched and multinucleate. Both are striated, so striations are not a difference between these two.
A third structural difference is the intercalated discs between cardiac cells, which skeletal muscle has not. Note that tiring and voluntary control are differences in behaviour, not structure — the question asks for structural ones.