区别挥发油与油脂常用的方法是
A．相对密度
B．溶解性
C．皂化值
D．油迹实验
E．比旋度
参考答案：D
解析： 本题考查挥发油与油脂的鉴别，间接考挥发油的通性。 挥发油：(1)颜色：挥发油大多为无色或淡黄色液体，有些挥发油含有奥类成分，或溶有色素，而显特殊颜色。(2)形态：挥发油在常温下为透明液体。低温放置，挥发油所含主要成分可能结晶析出，这种析出物习称为“脑”，如薄荷脑、樟脑等。(3)气味：挥发油具有特殊的气味，大多数为香味。也有少数为挥发油具有异味，如鱼腥草挥发油具有不愉快的臭味。(4)挥发性：挥发油均具有挥发性，可随水蒸气蒸馏，这是挥发油的重要性质，可以此区别脂肪油。
完型填空（15分） I have had thousands of classes since I started school nine years ago. But only one _1_ was the most important. It happened last term just after I had got a _2_ result in an exam. I was sad and had lost my confidence. I decided to go to a class which can tell me how to be_3_. The speaker walked into the room. But he did not start talking _4_ a teacher. Instead, he held up a twenty Yuan note(钞票)! “Who wants this?” he asked. Unsurprisingly, _5_ of us in the class held up our hands. The speaker smiled. Then he put up the note on the blackboard and asked the same question. Again, we all put up our hands. The speaker smiled again, but _6_nothing. Suddenly, he threw the note onto the floor! Then he asked the same _7_ a third time. I didn’t _8_ what the speaker was doing. Why was he asking the same question again and again? I didn’t know what to do. I wanted the note, _9_ I put my hand up again. After a while, he _10_ the note and started to laugh. “You have all just told me how to become successful,” _11_ said to us with the note in his hand. “The note is worth twenty yuan. It is _12_ worth twenty yuan, even though I throw it on the floor. You are like the note. No matter _13_ happens to you, you still have your worth.” When I heard those words, I was deeply moved. Suddenly, I _14_ I was worth a lot. I may have done badly in an exam, but it doesn’t _15_ I can’t do well in the future. If I believe in myself, I will be successful!
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