在含皂苷的乙醇溶液中分次加入乙醚或乙醚-丙酮混合液可使极性有差异的皂苷逐段沉淀出来的方法是( )
A．结晶法
B．专属试剂沉淀法
C．分级沉淀法
D．盐析法
E．分馏法
参考答案：C
解析： ①结晶法：化合物由非晶形经过结晶操作形成有晶形的过程称为结晶。结晶法是纯化物质最后阶段常采用的方法，其目的是进一步分离纯化，是利用混合物中各成分在溶剂中的溶解度不同达到分离的方法。②专属试剂沉淀法：某些试剂能选择性的沉淀某类成分，称为专属试剂沉淀法。③分级沉淀法：在混合组分的溶液中加入与该溶液能互溶的溶剂，改变混合组分溶液中某些成分的溶解度，使其从溶液中析出。改变加入溶剂的极性或数量而使沉淀逐步析出称为分级沉淀。④盐析法：在混合物的水溶液中加入易溶于水的无机盐至一定浓度或饱和状态，使其中药成分在水中溶解度降低而析出，或用有机溶剂萃取出的方法称为盐析法。⑤分馏法：是利用混合物中各成分的沸点不同而进行分离的方法。适用于液体混合物的分离。
Directions: There are 4 passages in this part. Each of the passages is followed by 5 questions or unfinished statements. For each of them there are 4 choices marked A, B, C and D. Choose the best one and mark your answer on the ANSWER SHEET with a single line through the center.
Passage One
| Andrea had never seen an old lady hitchhiking before. However, the weather and the coming darkness made her feel sorry for the lady. The old lady had some difficulty in climbing through the car door, and pushed her big brown canvas shopping bag down onto the floor under her feet. She said to Andrea, in a voice that was almost a whisper, "Thank you dear - I’m just going to Brock Bourne" Something in the way the lady spoke, and the way she never turned her head, made Andrea uneasy about this strange hitchhiker. She didn’t know why, but she felt instinctively that there was something wrong, something old, and something dangerous. But how could an old lady be dangerous It was absurd. Careful not to turn her head, Andrea look sideways at her passenger. She studied the hat, the dirty collar of the dress, the shapeless body, and the arms with their thick black hairs. Thick black hairs Hairy arms Andrea’s blood froze. This wasn’t a woman. It was a man. At first, she didn’t know what to do. Then suddenly, an idea came into her racing, terrified brain. Swinging the wheel suddenly, she threw the car into a skid, and brought it to a halt. "My god!" she shouted. "A child! Did you see the child I think I hit her. " The "old lady" was clearly shaken by the sudden skid. "I didn’t see anything dear," she said. "I don’t think you hit anything. " "I am sure it was a child!" insisted Andrea. "Could you just get out and have a look Just see if there is anything on the road" she held her breath. Would her plan work It did. The passenger slowly climbed out to investigate. As soon as in front of her vehicle, Andrea gunned the engine and accelerated madly away, and soon she had put a good three miles between herself and the awful hitchhiker. It was only then that she thought about the bag lying on the floor in front of her. Maybe the bag would provide some information about the real identity about the man. Pulling into the side of the road, Andrea opened the heavy bag curiously. It contained only one item — a small hand axe, with a razor-sharp blade. The axe, and the inside of the bag, were covered with the dark red stains of dried blood. Andrea began to scream. |
Andrea looked in the passenger’s bag to ______.
A．examine what was in it
B．find out where the passenger lived
C．use the passenger’s tools
D．find out who the passenger was