Which statement from fdr's speeches uses parallel structure?

a. no matter how long it may take us to overcome this premeditated invasion, the american people in their righteous might will win through to absolute victory.
b. admittedly the damage is serious. but no one can say how serious.
c. american ships have been sunk; american airplanes have been destroyed.
d. i do not think any american has any doubt of our ability to administer proper punishment to the perpetrators of these crimes.

I'd say that the statement from FDR's speeches that uses parallel structure is C. American ships have been sunk; American airplanes have been destroyed.
Both of these independent clauses use the passive form of the verb - in the first clause, the passive form of the verb to sink is used, and in the second, of the verb to destroy.
A parallel structure means that throughout a sentence, the same form of words is used, and given that here both sentences have passive forms, I'd say C is the correct answer.