问题
选择题
I _____ frustrated when I wasn't sure of the correct answer. [ ]
A. may be
B. used to
C. used to be
D. use to be
答案
答案：C
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I _____ frustrated when I wasn't sure of the correct answer. [ ]
A. may be
B. used to
C. used to be
D. use to be
答案：C