题目

若角α的终边与角β的终边关于直线y=x对称则α+β等于(    )A.2kπ,k∈Z      B.2kπ+π,k∈Z        C.2kπ           D.+2kπ,k∈Z 答案：D As we all know, two thirds of the earth’s surface is water, ___ a lot of fish.A．providedB．providingC．which providesD．it provides