Frequently, attention in an equilibrium situation is confined to a plane. an example would be a ladder leaning against a wall, which is in danger of slipping only in the plane perpendicular to the ground and wall. by orienting a cartesian coordinate system so that the x and y axes are in this plane, choose which of the following sets of quantities must be zero to maintain static equilibrium in this plane. a.\sum f_x and \sum \tau_z and \sum f_yb.\sum f_z and \sum \tau_x and \sum \tau_yc.\sum \tau_x and \sum f_x and \sum \tau_y and \sum f_yd.\sum \tau_x and \sum f_x and \sum \tau_y and \sum f_y and \sum \tau_z