题目

He was told that it would be at least three more months ___________he could recover and return to work.   A. when               B. before                    C. since                  D .that   答案：B如图为一圆柱形的玻璃棒过中心轴线的剖面图，该玻璃的折射率为n=，现有一束光线l 从AB面射入，入射角θ=60°，则折射角α=______，该束光线能否从 AD边射出______（填“能”或“不能”）