What does the term unauthorized absence (ua) mean? A. It was the term for someone being late for a drill or march.
B. It was the term for soldier that came back late for leave.
C. It was the term for a deserter of the unit -- a soldier who left without permission to go.

C

Explanation:

Though I would argue that deserter is a different term for someone who left a unit an unauthorized absence is someone who left without permission to do so.  

the completion of the erie canal spurred the first great westward movement of american settlers, gave access to the rich land and resources west of the appalachians and made new york the preeminent commercial city in the united states.