问题
选择题
The boy caught _____ the flowers was fined. [ ]
A. to pick
B. picking
C. to have picked
D. having picked
答案
答案：B
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The boy caught _____ the flowers was fined. [ ]
A. to pick
B. picking
C. to have picked
D. having picked
答案：B
金属烤瓷桥烧结完成后发现瓷表面出现龟裂现象，其原因是（）