题目

在实验步骤中，需用清水冲洗或漂洗以洗去药液的实验是                          ①探究酵母菌的呼吸方式           ②观察植物根尖细胞的有丝分裂③观察DNA、RNA在细胞中的分布  ④叶绿体色素的提取和分离 A. ②③         B. ②④        C.①③       D. ①④ 答案：A阅读理解。     It was 3:12 a. m. when nine-year-old Glenn Kreamer awoke to the smell of burning. Except for the crackling of flames somewhere below there was not a sound in the two-storey house at Baldwin, Long Island. With his father away on night duty at a local factory, Glenn was worried about the safety of his mother, his sister Karen, 14 and his 12-year-old brother Todd. He ran downstairs through the smoke-filled house to push and pull at Karen and Todd until they sat up. Then he helped each one through the house to the safety of the garden. There, his sister and brother, taking short and quick breaths and coughing, collapsed on the lawn.      The nine-year-old boy raced back into the house and upstairs to his mother's room. He found it impossible to wake her up. Mrs. Kreamer, a victim of the smoke, was unconscious (无意识的), and there was nobody tohelp Glenn carry her to the garden. But the boy remained calm and, as a fireman said later, "acted with all theself-control of a trained adult."      On the bedroom telephone, luckily still working, Glenn called his father and, leaving Mr. Kreamer to telephone the fire brigade and ambulance service, got on with the task of saving his mother.       First he filled a bucket with water from the bathroom and threw water over his mother and her bed. Then,with a wet cloth around his head he went back to the garden.       He could hear the fire engine coming up, but how would the firemen find his mother in the smoke-filled house where flames had almost swallowed up the ground floor?      Grasping firmly a ball of string (线绳) from the garage, Glenn raced back into the house and dashed upstairs to his mother's room. Tying one end of the string to her hand, he ran back, laying out the string ashe went, through the hall and back out into the garden.      Minutes later he was telling fire chief John Coughlan:"The string will lead you to mother." Mrs. Kreamer was carried to safety as the flames were breaking through her bedroom floor. 1. Why did Glenn run downstairs first? [     ]A. He wanted to find out what was happening.B. He was worried about his mother's safety.C. He wanted to save his sister and brother. D. He went to see if his father had come back from work. 2. How did Glenn help the firemen to save his mother? [     ]A. By throwing water all over her and her bed. B. By carrying her to safety with his brother. C. By pushing and pulling at her.D. By tying a string to her hand. 3. What did Glenn do to protect himself? [     ]A. He put a wet cloth around his head.B. He threw water all over himself. C. He hid himself in the bathroom. D. He rushed out to the lawn. 4. Glenn saved his family because _____. [     ]A. his father had taught him to do so on the phone B. he had learned something about first aid C. he had dealt with the emergency calmly and wisely D. he had followed his mother's instruction