读下图 “地球公转示意图”，图示季节，可能出现的现象为(    )

下列有关声现象的说法中，正确的是（     ）

根据短文括号内所给汉语意思，在空白处写出单词的正确形式。每空一词

 Last ____ (圣诞节) Day, when I was at the street ____ （角落）, a car ____ （经过） by. The car stopped in front of me. A woman looked out of the car and asked me  ____ （有礼貌地）, “Excuse me, could you tell me the right direction to the  station?” Oh, my god! She was my old classmate. She used to be a shy girl. She didn’t ____（敢于）to speak in ____ （公众）. But her English was good and she did well in the ____ （发音） and the ____ （语法）. I____ （羡慕） her very much. Finally we had a happy  ____ （谈话） and I told her the way to the station.

如图是一个以点A为对称中心的中心对称图形，若∠C =90°，∠B = 30°，AC = 1，则BB′的长为（  ）

若一个三角形的任意两边都不相等，则称之为不规则三角形。用一个正方体上的任意三个顶点构成的所有三角形中，不规则三角形的个数是（  ）