问题
单项选择题
暂时性错胎发生机制是
A．恒切牙萌出初期，出现轻度拥挤现象，可能因恒牙较乳牙大，随着颌骨的增大和乳磨牙与前磨牙的替换等变化可自行调整
B．唇系带异常可造成上中切牙之间出现间隙
C．以上都不是
D．咬上唇习惯容易形成前牙反牙合，下颌前突及近中错胎等畸形
E．多生牙占据了恒牙的位置，常引起恒牙的错位萌出
答案
参考答案：A
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暂时性错胎发生机制是
A．恒切牙萌出初期，出现轻度拥挤现象，可能因恒牙较乳牙大，随着颌骨的增大和乳磨牙与前磨牙的替换等变化可自行调整
B．唇系带异常可造成上中切牙之间出现间隙
C．以上都不是
D．咬上唇习惯容易形成前牙反牙合，下颌前突及近中错胎等畸形
E．多生牙占据了恒牙的位置，常引起恒牙的错位萌出
参考答案：A
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| Jack 1 in the country and he loves 2 in the river near his house, but his father gets a job in a big city and he moves there 3 his family. Their new house has a garden, but the garden is small. Jack 4 very happy. "Is there a river 5 here?" He is asking his mother 6 the first morning. His mother is answering, "No, there isn't, but there is a beautiful park nearby and there is a pool in it. We 7 there this afternoon." Jack is happy now. After lunch, Jack and his mother go to the park. Jack wants 8 near the pool, but there is a sign in front of it. His mother reads it to him. "Warning (注意), this pool is dangerous, 367 people have fallen into it (已掉入)." Jack looks into the pool 9 and he says, "But I can't 10 them." | ||||
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