在平面力系中所有力作用线汇交于一点的力系，有（）个独立的平衡方程

问答题The underlined part in Paragraph 2 most probably means that games can.() A describe life in an exciting way B change your life experiences C make learning life skills more interesting D change people's views of sporting events

问答题Through playing hide-and-seek,children are expected to learn to_.() A be a team leader B obey the basic rules C act as a grown-up D predict possible danger