(A) The importance of snowfall for Mount Rainier.

　　(B) The steam caves of Mount Rainier.

　　(C) how ice covers are destroyed .

　　(D) The eruption of Mount Saint Helens in 1980.

　　46 The word "they" in line 2 refers to

　　(A) fields

　　(B) intervals

　　(C) eruptions

　　(D) enemies

　　47 According to the passage long periods of volcanic inactivity can lead to a

　　volcanic cone's

　　(A) strongest eruption

　　(B) sudden growth

　　(C) destruction

　　(D) unpredictability

　　48 The second paragraph mentions all of the following as necessary elements in

　　the creation of

　　steam caves EXCEPT

　　(A) a glacier

　　(B) a crater

　　(C) heat

　　(D) snow

　　49 According to the passage, heat from Mount Rainier's summit craters rises from

　　(A) crystalline ice

　　(B) firns

　　(C) chambers

　　(D) fumaroles

　　50 In line 26 "smothering" the caverns means that they would be

　　(A) eliminated

　　(B) enlarged

　　(C) prevented

　　(D) hollowed

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