大学英语四级考试阅读笔记(22)

Questions 61 to 65 are based on the following passage:
61. By "... challenges explanation" ( Line 2, Para. 1) the author means that _________
A) no explanation is necessary for such an obvious phenomenon
B) no explanation has been made up to now
C) it' s no easy job to provide an adequate explanation
D) it' s high time that an explanation was provided
注：词汇题

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