题目

California is home to 4, 426 species of plants, and nearly half of_________ are found nowhere else． A．which           B．them         C．what             D．that 答案：B已知等差数列{an}的前n项和为Sn，若=a1+a2009，且A、C三点共线（O为该直线外一点），则S2009等于（ ）A．2009B．C．22009D．2-2009