题目

数列的前项和，则通项公式            ． 答案：；   20．16．Mr．Chaplin can't be here because he'sC．     A．gone to England            B．ill                    C．gone to America17．There is an importantBexam today．     A．Math        B．English               C．Chinese18．The exam ends atAo'clock this morning．     A.11           B.9       C.719．If there is a difficult question，you shouldC．     A．write it clearly       B．answer it first    C．go on to the next one and come back to it later．20．Don't leave questions unanswered； sometimes aAmay help you get points．     A．guess                     B．guest                 C．gate．