将直线x+y-1=0绕点(1,0)顺时针旋转后,再向上平移一个单位,这时恰好与圆:x2+(y-1)2=R2相切,则正数R等于________________.
“低碳生活”已成为时髦的话题，保护植被和大面积绿化是降低大气中二氧化碳含量的有效方法，对改善人类的生存环境有重大意义，其原因之一是植
在种子萌发时，最先突破种皮的是（ ） A．胚芽 B．胚轴 C．胚根
On a cold November afternoon, my mother and I were walking home from a pizza store. We were dressed 1 and equipped with the rented video we had been 2 to watch. I was feeling a little
《明经世文编选录》载：“番中本无盐硝、火药、亦无铳炮器具，后因中国之人接济往来，私相教习，违犯严禁，将带出境，以济番人之用……若今明
“氯气在通常情况下是一种黄绿色有剌激性气味的气体”这句话说明的是氯气的( )A．物理变化B．化学变化C．物理性质D．化学性质
It was a market day, so people and traffic had been pouring into the town since early morning． 1 it was an old town, even the main street was very 2 and soon became overcrowded． There wa
下列物质的用途或用法与其理由说明相一致的是 ( ) A．通常情况下输电电缆用铝制成，是因为铝是导电性最好的金属 B．贴身衣物常选择棉制品，是
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