A. their parents B. some good neighbors C. many other penguins D. their chicks 参考答案:C 答案解析:根据文章第一句话,Penguins live together in large and busy colonies.表明企鹅是群居生活的,因而选项[C]正确。
第21题: [填空题]Jim’s parents encouraged him to study both the constructivist math and traditional math. 参考答案:N 答案解析:[解析] “Jim,however,placed the credit elsewhere. His parents,an engineer and an educator, covertly tut
第25题: [单项选择]主动脉在维持舒张压中起重要作用,主要是由于主动脉 A. 口径大 B. 管壁厚 C. 管壁有可扩张性和弹性 D. 血流速度快 E. 对血流的摩擦阻力小 参考答案:C 答案解析:[解析] 由于主动脉和大动脉管壁具有较大的可扩张性,所以左心室一次收缩所射出的血量,在心缩期内只有约1/3流至外周,其余2/3被暂时贮存在主动脉和大动脉内,使主动脉和大动脉进一步扩张,主动脉压也随着升