题目

设等差数列的前项和为，点在直线上，则（   ） A．               B．         C．          D． 答案：B ____paragraph is a group of sentences about some related subject. Readers must know what the main idea of ___paragaph is in order to understand ___information they are reading. A．The ,a ,the B．A,the ,the C．A,a the D．The ,the ,the