题目

 After the accident, the police __ __ to help the wounded people.      A. was called in                             B. were called in       C. called on                                  D. called 答案：B计算题（5分）体积是30cm3的空心铜球质量m=178g，空心部分注满某种液体后，总质量m总=314g，问注入的液体的密度？（ρ铜=8.9×103㎏/m3）