问题
单项选择题
某患者，一上前牙牙冠大部缺损，作桩冠修复时，根管制备的长度应达根长的
A．1/5～2/5
B．3/5～4/5
C．1/4～1/2
D．1/2～1/3
E．2/3～3/4
答案
参考答案：E
解析：桩核中桩的长度应达到根长的2/3～3/4。
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某患者，一上前牙牙冠大部缺损，作桩冠修复时，根管制备的长度应达根长的
A．1/5～2/5
B．3/5～4/5
C．1/4～1/2
D．1/2～1/3
E．2/3～3/4
参考答案：E
解析：桩核中桩的长度应达到根长的2/3～3/4。
Sarah came running in. She shouted happily, "Look what I ____36_____." She put a snake skin on the newspaper I was reading and it came so suddenly that it caused me to ____37_____. "Mom, look! Isn't it ____38_____?" said my seven-year-old daughter. I ____39_____ the snake skin and thought that it really wasn't pretty. Everything children see ____40_____is full of beauty in their eyes; they see only ____41_____ and excellence in the world until educated. "____42_____ did the snake do this?" Sarah asked. I tried to seize the ____43_____ to teach my children that there was almost always something beyond the obvious. I wanted to tell them that there was something else going on ____44_____ what they saw in front of them. "Snakes shed (蜕) their skin because they need to renew themselves," I ____45_____. "Why do they have to renew themselves?" Sarah asked. My son Robert laughed and said, "Because they don't ____46_____ what they are and they want to be someone else." I politely ignored him and said that by shedding skins, we could ____47_____ the hidden reality. "We often need to shed our skin, those coatings that we ____48_____ ourselves with," I said to my children, who listened very ____49_____, with their eyes wide open. "This snake ____50_____ needs this skin. It is probably too hard for him, or he probably doesn't think he looks as ____51_____in it as he once did. It's like buying a new ____52_____." I'm sure this explanation will not ____53_____ the naturalists. But Sarah was getting to understand that renewal is part of ____54_____. She should learn from it what we need to keep and what we need to ____55_____.
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