Question

Yesterday he sold out all his stamps at ____ he thought was a reasonable price

A. that B. which C. what D. as

Answer 1

俊狼猎英团队为您解答。
C. what 为正确选项。
what was a reasonable price 是一个宾语从句，做at 的宾语，而 he thought 是插入语，省去不影响句子的完整性。
祝你进步！

Answer 2

C
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祝你学习进步，更上一层楼！(*^__^*)