第4题: [单项选择]甾体皂苷元的最基本结构特点是() A. 有30个碳 B. 有5个环 C. 有环戊烷骈多氢菲结构 D. C17为不饱和内酯环取代 参考答案:C
第5题:[单选题]When the center tank is empty,in AUTO MODE,the center tank transter valves A.A、must be manually switched OFF after 5 minutes B.B、stop automatically and winp tank pumps start running C.C、close automatically after a time delay of 5 minutes 参考答案:C