中国大学MOOC: Historians are still mystified by the question____ some ancient civilizations disappeared suddenly in history.
中国大学MOOC: Historians are still mystified by the question____ some ancient civilizations disappeared suddenly in history.
Historians are still mystified by the question____ some ancient civilizations disappeared suddenly in history.( ) A: that B: how C: that is D: is how
Historians are still mystified by the question____ some ancient civilizations disappeared suddenly in history.( ) A: that B: how C: that is D: is how
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