若3,a,b,c,15成等差数列,则a+b+c=____
I took about two hours (小时) my homework.
(2016•宜宾)读我国四个城市气温降水资料图,图中③城市所属气候类型是( )
传染病是人类健康的大敌,人类与传染病进行了长期不懈的斗争,请回答: