Mountain climbing ________ be very tiring, and many people feel sick ________ the atmosphere gets thinner.
A.may; while | B.can; as | C.must; though | D.should; for |
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Mountain climbing ________ be very tiring, and many people feel sick ________ the atmosphere gets thinner.
A.may; while | B.can; as | C.must; though | D.should; for |