题目

Tom wanted to play football with his friends in the street, but his father told him＿＿＿＿＿.A.not to     B.not to do  C.not do it     D.do not to 答案：A 解析: tell him not to (play football with his friends in the street.)对于正数x，规定f1（x）=, f2（x）=，例如f1（1）=1，f2（1）=，计算f1（1）f2（1）+ f1（2）f2（2）+ f1（3）f2（3）+ …f1（100）f2（100）=         。