_______ I went to the South Lake in Hanzhong, I was deeply impressed with its beautiful scenery. A. For the first time B. The first time C. At first D. It was the first time 答案:B某校高中生共有900人,其中高一年级300人,高二年级200人,高三年级400人.现采用分层抽样抽取容量为45的样本,那么高一、高二、高三各年级抽取的人数分别为 ( ) A.15、5、25 B.15、15、15 C.10、5、30 D.15、10、20