The primary purpose of runway end identifier lights, installed at many airfields, is to provide _______ ．
A.a warning of the final 3, 000 ft of runway remaining as viewed from the takeoff position
B.rapid identification of the approach end of the runway during reduced visibility
C.a warning of the final 1, 000 ft of runway remaining as viewed from the approach position
D.rapid identification of the primary runway during reduced visibility
正确答案是B