慢性消化性溃疡穿孔多见于（）
A.胃前壁溃疡
B.胃后壁溃疡
C.十二指肠球前壁溃疡
D.十二指肠球后壁溃疡
E.十二指肠球后溃疡
参考答案：D
“x与y的差”用代数式可以表示为（ ）。
China’s third manned spaceship Shenzhou Ⅶ was launched and three pilots successfully ____ the mission.
A．acquired
B．accomplished
C．achieved
D．attained
