31. According to the passage, what happens during an ice age?
(A) Rock strata are recognized by geologists.
(B) Evidence of foreign materials is not found.
(C) Ice covers a large portion of the Earth’s surface.
(D) Ice melts six times.
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統計: A(29), B(9), C(240), D(20), E(0) #1368660
統計: A(29), B(9), C(240), D(20), E(0) #1368660