The correct option is C II and III
In structure I, neither cycloheptatriene nor cyclopentadiene alone is aromatic.
In structure II, both the rings are aromatic because both seven (6 π-electrons) as well as five membered (6 π-electrons) rings are aromatic. Hence II is the most stable structure.
In structure III, both the rings are anti-aromatic because both seven (8 π-electrons) as well as five membered (4 π-electrons) rings are anti-aromatic. Hence III is the least stable structure.