在“探究凸透镜成像规律”的实验中,所选用凸透镜的焦距为10cm.
若最简二次根式1+a 与2 是同类二次根式,则a的值为( )
— The problem is ________ difficult. I can't work it out.
— Try again, please.
洋葱鳞片叶表皮属于( )