答案：D

题目分析：句意：Bo先生已经离开了半个月了，两个月之后他将回来。句中有表一段时间的状语for half a month，谓语动词要有延续性，leave 改为be away,故选D.

点评：延续性动词与表示一段时间的时间状语连用。非延续性动词向延续性动词的转变熟记一下几个：

leave --- be away,  borrow --- keep,  buy --- have,  begin/start --- be on,      die --- be dead, leave --- be away from, fall asleep --- be asleep