题目

_____ any change about the date, please tell me immediately. A. Will there be    B. Should there be    C. There will be    D. There should be  答案：B等差数列{an}中，a1+a2+…+a50=200，a51+a52+…+a100=2700，则a1等于（ ）A．-1221B．-21.5C．-20.5D．-20