在母质、生物、气候、地形和时间各种自然因素共同作用下形成和发育的肥力是（）
A.自然肥力
B.人为肥力
C.有效肥力
D.潜在肥力
参考答案：A
—Why are you standing there, Kangkang?
—I can't see the blackboard clearly. Two tall boys are sitting ______ me. [ ]
A. behind
B. next to
C. in front of
D. beside
患者李某，40岁，急性心肌梗死病史半年，血压持续在160/’95mmHg左右，其降压药宜选用( )
A．甲基多巴B．利血平C．呋塞米D．倍他乐克E．哌唑嗪
