题目

The sale usually takes place outside the house, with the audience______on benches, chairs or boxes. A . having seated B . seating C . seated D . being seated 答案：C 在“探究杠杆的平衡条件”的实验中，首先调节杠杆两端的________，使杠杆在________位置平衡．这样做的目的是使杠杆的动力臂与________都恰好在杠杆上，便于在杠杆上直接读出________．