do some exercise还是exercises

do some exercises还是do some exercise对

exercise作名词指“锻炼”时,是不可数名词.应该作 do some exercise

exercise作名词指“习题”时,后面跟in和科目名称,或on/in和科目的部分的名称,如an exercise in English grammar（英语语法习题）,an exercise on/in the construction of conditional sentences（条件句结构的习题）；

exercise如果泛指“锻炼，练习”的意思时，是不可数名词。