第3题: [单项选择]Lehman Caves are______. A. about a kilometre each B. separated from each other C. rooms made of limestone D. what interest visitors most 参考答案:C 答案解析:[解析]从文章中第四段第二句：These caves are a group of large underground rooms made of limestone．得知。故本题答案为C。
第19题: [填空题]A depressed person might feel hopeless, helpless and overwhelmed if he is inclined to ______ of life. 参考答案:exaggerate negative aspects 答案解析:[题眼] A depressed person might feel hopeless. helpless and overwhelmed if he is inclined to______ of
第20题: [单项选择]心肌不会产生强直收缩的原因是______。 A. 心肌的收缩呈“全或无”式反应 B. 心肌有特殊传导组织 C. 心肌肌浆网不发达，贮存Ca2+比较少 D. 心肌细胞兴奋后有效不应期长 参考答案:D 答案解析:[解析] 明确肌肉强直收缩的概念；明确心肌兴奋性变化与收缩的关系。 给骨骼肌两次或两次以上的阈上刺激，若后一次刺激落在了前一次刺激的舒张期或收缩期，就会出现不完全强直收缩或完全强直收缩。而心肌细
