Ⅳ. 词汇运用（共10小题；每小题1分，满分10分）

51. Tom's work at school is above the __________  . (平均)

52. His brave act            admiration. (应得)

53. There is no             that we will be successful. (怀疑)

54. I must            to you for being late. (道歉)

55. He            the house at $800,000 . (估价)

56. The memorial is            on a cliff overlooking the beach and the channel. (位于)

57. Many questions also            in the cloning of dinosaurs. (出现)

58. He has about the same            as his brother. (身材)

59. They            to meet again at 8 o’clock.. (约定)

60. He is always            from the regular meeting. (缺勤)

妊娠期龈炎的直接病因是

A．妊娠

B．牙石

C．不良卫生习惯

D．牙菌斑

E．不良修复体