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.
Threateningly
We can tell that because the dogs are huddled together in fear, there's some sort of danger. Also the snarling suggests they are under caution or going on defense from some danger; they feel threatened.
The author's attitude toward the subject on which he/she is speaking.
attitude is everything like if you were hanging out with your best friend and your feeling down that just makes everyone else in a bad mood.
