People are riding around on snowmobiles.
People are riding snowmobiles at high speeds.
Not all people riding around on snowmobiles are doing so in high speeds.
exists e1 x1 x2.(r_around(e1) & on(e1,x2) & n_snowmobile(x2) & Actor(e1,x1) & v_ride(e1) & n_people(x1))
exists e1 s1 x1 x2 x3.(at(e1,x3) & n_speed(x3) & a_high(s1) & Theme(s1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_snowmobile(x2) & n_people(x1))