—Excuse me. Where is school library? —This way, please.
小明在探究“光反射时的规律”时将一块平面镜放在水平桌面上,再把一张纸板放置在平面镜上.
如图为“北京市气温曲线和降水柱状图”,据图说出发展农业的有利条件是( )