问题补充：
28. Think after you read .
A. which words do you need to look up
B. you need to look up which words
C. which words need you look up
D. which words you need to look up
答案：
A. which words do you need to look up
B. you need to look up which words
C. which words need you look up
(答案→)D. which words you need to look up
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