【单选题】
13.The monument(里程碑) was built in honor of the explorer who was believed ____the river.
①
to have discovered
②
to have been discovered
③
to discover
④
having been discovered
【多选题】
延安时期，毛泽东曾指出：文艺为工农兵服务，这一方针成为文艺史上的里程碑。毛泽东还说（）。
①
A.知识分子向群众学习
②
B.外来的干部向本地的干部学习
③
C.革命老同志向小同志学习
④
D.洋包子要向土包子学习