Mark Twain was restless when he was young and moved a lot， first eastward as a journeyman printer， up and down the Mississippi as（）.

Mark Twain was restless when he was young and moved a lot， first eastward as a journeyman printer， up and down the Mississippi as（）.
A、a steamboat pilot
B、a guard
C、a servant
D、a sailor
正确答案：A