To our surprise，the stranger to be an old friend of my mother's.
A. turned up
B. set up
C. set out
D. turned out
网友回答
A. turned up
B. set up
C. set out
(答案→)D. turned out
解析：句意：令我们惊奇的是，那个陌生人结果却是我母亲的一位老朋友。turn up“调高，露面”；set up“建立，竖起”；set out“出发，动身”；turn out“证明是，结果是”。故选D项。