问题补充：
He has gained rich work experience there and is showing great progress.
A. a; a
B. a; /
C. /; a
D. /; /
答案：
A. a; a
B. a; /
C. /; a
(答案→)D. /; /
解析：冠词考查题。第一空experience作“经验”讲为不可数名词其千不用冠词，作“经历”讲为可数名词；第二空progress“进步”不可数名词其前不用冠词。句意：他在那获得了丰富的工作经验并且表现出很大的进步。
