_________a stone tower near the old pine tree.

A．It used to be

B．There used to be

C．There used to have

D．It is used to be

与大气压力作用无关的因素是（）

A.基托与黏膜的接触面积

B.基托与黏膜的密合度

C.义齿边缘封闭效果

D.后堤区的范围大小

E.基托的材料