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问题 单项选择题

某高龄个体，牙周组织表现为老年性萎缩，牙根部分暴露，无松动，牙冠磨耗严重，其原因是（）

A.咬合畸形

B.夜磨牙

C.深覆

D.发育异常

E.正常生理现象

答案

参考答案：E

完形填空

It was my first day in Hangzhou, the Chinese city famous for its natural beauty and history and I didn't have much time to spare. I wanted to see 小题1: much of the city as possible in the two days 小题2: I was to return to Guangzhou. My first task was to decide where to go and  小题3: to get there. I took out my guide book in which there was a lot of information about the city's well-known tourist  小题4: (attract) and started to read. At that moment an attractive young lady 小题5: noticed my book came up to me and introduced  小题6: . She said her name was Miss Bai she and kindly offered to show me 小题7: the city. I was delighted and was about to accept her proposal __小题8:__she suggested we first  小题9:  (go)to the West Lake and walk along the Broken Bridge. I quite liked the idea of visiting the West Lake but wasn't so sure about crossing the Broken Bridge . 小题10: it was broken, did she expect me to jump across? And I couldn't swim, so if I fell in then I would drown. That was definitely not an attractive idea so I politely declined her invitation,closed my book and walked away.
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单项选择题

下列哪种物质不是嘌呤核苷酸从头合成的直接原料

A．甘氨酸

B．天冬氨酸

C．谷氨酸

D．CO2

E．一碳单位
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