47. A man is nearsighted and cannot see things clearly beyond 110 cm from his eyes. What is the focal length of the contact lenses that will enable him to see very distant objects clearly?
(A) 50 cm
(B) -50 cm
(C) -110 cm
(D) 110 cm
(E) -30 cm.
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統計: A(0), B(0), C(14), D(1), E(1) #3093888
統計: A(0), B(0), C(14), D(1), E(1) #3093888