①京师大学堂②安庆内军械所③江南制造总局④废除科举制度⑤兴办新式学堂
A:①②③
B:①③④
C:①④⑤
D:③④⑤
—I think my Maths teacher is working hard. He teaches us very .
—Yes, but he can't come today. He doesn't feel .
魏晋南北朝以来,全国经济重心出现南移的趋势,到_______时,南方已成为全国经济的重心。( )
一实验小组用某一单色光做双缝干涉实验时,在距离双缝为1.0m处的光屏上,测得1至5条亮纹间的距离为7.6mm.已知所用的双缝间距离为0.25mm.