The correct answer is one main clause.
This means that there is only one verb in the sentence, which in this case is the verb 'was.' Even though drive is also a verb, in this context it is used as an adjective driven (participle form of the verb to drive) and is thus not considered to be a verb. This means that there are no subordinate clauses but rather just one main clause.
They begin bombarding the castle
To figure out point of view (POV), look for the PRONOUNS.
First person: told FROM the narrator's/author's point of view: uses the pronoun "I"
Second person: told directly TO the reader: uses the pronouns "you/yours" (for what it's worth, this POV is rare.)
Third person: told as an observation ABOUT the characters: uses the pronouns "he/she/it/they/his/hers/its/theirs"
