问题
单项选择题
若提取药材中的原生苷，除了采用沸水提取外，还可以选用
A．热乙醇
B．乙醚
C．酸水
D．氯仿
E．冷水
答案
参考答案：A
解析：在植物体中，苷类往往是与能水解苷的酶共存，因此，在提取原生苷时，首先要设法破坏或抑制酶的活性，以避免原生苷被酶解，常用的方法是采用甲醇、乙醇或沸水提取。
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若提取药材中的原生苷，除了采用沸水提取外，还可以选用
A．热乙醇
B．乙醚
C．酸水
D．氯仿
E．冷水
参考答案：A
解析：在植物体中，苷类往往是与能水解苷的酶共存，因此，在提取原生苷时，首先要设法破坏或抑制酶的活性，以避免原生苷被酶解，常用的方法是采用甲醇、乙醇或沸水提取。
Not many foreigners can say that they have lived in China for as long as I have. Perhaps some can hack(应对) it for about two or three years and then they want to either go back home or move on to another country. As for me, I cannot get 36 of this place. I love it here so much and I honestly believe that I am very comfortable here. It feels just like 37. And, here 38 the story. It was August 2001 and I had just said 39 to my family and friends as I 40 to Los Angeles International Airport to catch my 41 to Incheon, South Korea which would then 42 me to Beijing. When I arrived in LA I was very excited and a little 43 because I didn't know what to 44 when I arrived in China. It 45 like receiving a wrapped gift and you had no idea what was in it 46 you opened it. As I 47 the Korean Airlines 48 desk I gave the attendant(空乘人员) my ticket. He looked at me and said, "I'm sorry, sir. This flight was yesterday." I was in 49 and lost for words. The attendant told me I had to wait several hours until they could 50 whether I could get onto another flight. I was so afraid at this time that I called my mother and frantically(狂乱地) told her," I missed my flight! I don't think I can go to 51! I'm better off going back to Washington, DC!" That's when she 52 I call my leader in China and ask whether I could still go there. Looking 53 all of the papers I found a phone number and called the Beijing office. 54, my leader was there and assured me I could still join the group. Also, KAL had a seat for me on the next flight. So, after 24 hours and a 55 in Korea, I arrived in Beijing. I don't know what my feeling was, but I wasn't tired because I had finally arrived and I just wanted to look around the city. As I traveled to the hotel in the car I saw all the wonderful buildings, friendly people and interesting sites. I was so happy to be here.
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为一直角三棱镜的截面，其顶角
，BC边长为a，棱镜的折射率为
，P为垂直于直线BCO的光屏。现有一宽度等于AB的平行单色光束垂直射向AB面，求在光屏P上被折射光线照亮的光带的宽度。
；
）