花岗岩山地有什么特点请列举出四个花岗岩名山。
参考答案:球状风化,形成巨大的浑圆多姿的巨石;差别风化,形成象形石峰;垂直节理发育,形成危崖峭壁;花岗岩名山:泰山、华山、黄山、千山。
存在于钙化的骨基质陷窝内的细胞为
A.成骨细胞B.骨细胞C.骨衬里细胞D.破骨细胞E.前成骨细胞
A ladder 25 feet long is leaning against a wall that is perpendicular to level ground. The bottom of the ladder is 7 feet from the base of the wall. If the top of the ladder slips down 4 feet, how many feet will the bottom of the ladder slip ?()
A.4
B.5
C.8
D.9
E.15