表示牙本质的发育和形成速率是周期性变化的是（） A.原发性牙本质 B.继发性牙本

丁酸是无色透明油状液体，有腐臭的酸味；乙酸乙酯是无色透明易挥发的液体，有果香味，易燃．但是，丁酸和乙酸乙酯的化学式都为C₄H₈O₂．请用所学的结构、性质等知识分析下列认识中正确的是（　　）

A．丁酸、乙酸乙酯都是无机化合物

B．两种化合物由于分子中原子排列方式不同，形成不同的分子结构，所以性质有差异

C．两种化合物的相对分子质量不同

D．两种化合物中碳、氢、氧三种元素的质量比为4：8：2

All her life, my mother wanted busy children. It was very important that her house should remain at all times clean and tidy.
You could turn your back for a moment in my mother’s house, leave a half written letter on the dining table, a magazine open on the chair, and turn around to find that my mother had "put it back where it belonged," as she explained. My wife, on one of her first visits to my mother’s house, placed a packet of biscuits on an end table and went to the kitchen to fetch a drink. When she returned, she found the packet had been removed. Confused, she set down her drink and went back to the kitchen for more biscuits, only to return to find that her drink had disappeared. Up to then she had guessed that everyone in my family held onto their drinks so as not to make water rings on the end tables. Now she knows better.
These disappearances had a confusing effect on our family. We were all inclined to forgetfulness, and it was common for one of us, upon returning from the bathroom, to find the every sign of his work in progress had disappeared suddenly. "Do you remember what I was doing" was a question frequently asked, but rarely answered.
Now my sister has developed a secondhand love of clean windows, and my brother does the cleaning in his house, perhaps to avoid having to be the one to lift his feet. I try not to think about it too much, but I have at this later time started to dust the furniture once a week.

My wife could not find her biscuits and drink in my mother’s house because ______.

A．she had already finished them
B．my mother had taken them away
C．she forgot where she had left them
D．someone in my family was holding them

卫兵队的领班员由（）担任，受（）领导。

A、班长、副班长；分队首长

B、班长、副班长；卫兵队队长

C、班长、副班长和士兵骨干；卫兵队队长

D、班长、副班长和士兵骨干；分队首长

甲亢病人术后病情平稳后宜取的体位是

A．去枕平卧位

B．低枕平卧位

C．半卧位

D．侧卧位

E．头低脚高位

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