题目

When ______ comes to research into heart disease and its effects on the body, we do not have adequate substitutes for the use of animals.    A. that          B. it                   C. this             D. what 答案：B 解析: 略3．挖一条水渠长36千米，七月份挖了全长的$\frac{1}{3}$，八月份挖了全长的$\frac{5}{12}$．（1）八月份比七月份多挖多少千米？（2）还剩多少千米没有修？