Answer:
A. As Mother drove, Father studied the road map.
Explanation:
Option A is correct. The dependent clause "as mother drove" introduces the sentence. It must be followed by a comma to separate it from the independent clause "Father studied the road map." In option C there should never be a comma after "as". In option D the comma separates the verb "studied" from the direct object "the road map" which isn't grammatically correct.
