题干

用标准NaOH滴定未知浓度的盐酸,酚酞为指示剂,造成测定结果偏低的原因可能是

A:未用标准液润洗碱式滴定管

B:滴定终点读数时,俯视滴定管的刻度,其它操作均正确

C:盛装未知液的锥形瓶用蒸馏水洗过,未用待测液润洗

D:滴定到终点读数时发现滴定管尖嘴处悬挂一滴溶液

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答案(点此获取答案解析)

B

同类题1

完形填空

    I had just arrived in this Asian country for a one-year teaching position. One day, I took the subway to visit some ancient palaces and temples in the downtown. The following account of what happened to me has taught me much about culture 1.

    Since all the 2 were taken, I stood. Suddenly, I felt someone pulling on my bag. 3 I probably was in someone's way, I moved over slightly. But in one quick motion(动作), I felt my bag removed from my back, and in a flash it was 4. I turned around to see who the thief was. I looked at the people standing behind me, but didn't see my bag or any 5. My heart sank and I began to 6.

    I glanced around the car only to find directly across from me was an elderly lady, and sitting on her lap was my 7. I tried to get it back from her lap. But as I began to 8 it up, she quickly grabbed(抓住) it back and held onto it. I looked around at the people standing beside me, and those sitting beside her, but no one took any 9 of the situation. Trying not to cause a(an) 10, I tried to negotiate through gestures. I used my hands as best as I could, but she 11 my requests for my bag and pointed to my back. She picked up my bag, showing how 12 it was. I finally began to understand. She was holding my bag to13 me.

    At the next stop, a middle-aged woman got on the crowded subway. Another elderly woman sitting down took her bag, 14 it on her lap. They didn't talk; 15 this older woman was more than pleased to sit with this stranger's bag on her lap throughout her journey.

    As the subway pulled into the main downtown station and I was getting ready to get off, the woman 16 handed me back my bag. But 17 I had a chance to thank her, she had disappeared into the crowd.

    Sadly, this considerate custom was more 18 to me than if I had been robbed. Everyone back home had heard of being robbed—that was 19 city behavior—but having a stranger hold onto someone's bag out of 20, in a city of twelve million people—that was truly unusual.

同类题5

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                                                                                                        中国的牛
      对于中国的牛,我有特别的尊敬感情。
      留给我印象最深的,要算上一回在田垄上的“相遇”。
      一群朋友郊游,我领头在狭窄的阡陌上走,怎奈迎面来了几头耕牛,狭道容不下人和牛,终有一方要让路。它们还没有走近,我们已经预计斗不过畜生,恐怕难免踩到稻田泥水里,弄得鞋袜又是泥又是水了。正在踌躇的时候,带头的那头牛在离我们不远的地方停下来,抬起头看看,稍迟疑一下,就自动走下田去,一队耕扣跟着它全走离阡陌,从我们身边经过。
      我们都呆了,回过头来,望着深褐色的牛队在路的尽头消失,忽然觉得自己受了很大的恩惠。
      中国的牛,永远沉默地为人做着沉重的工作。在大地上,晨光或烈日下,它拖着沉重的犁,低头一步又一步,拖出了身后一列又一列的松土,好让人们下种。等到满地金黄的时侯,它可能还得担当搬运负重的工作。或终日绕着石磨,朝着一个方向,走不计程的路。
      在它的默默劳动中,人便得到应有的收成。那时侯,也许,它可以松一肩重担,站在树下,吃几口嫩草。偶尔摇摇尾巴,摆摆耳朵,赶走飞附在身上的苍蝇,已经算是最闲适的生活了。
      中国的牛,没有成群奔跑的习惯,永远沉沉实实的。它们不像印席的牛,负着神圣之名,摇着尾巴在大街上闲荡。它们不像荷兰乳牛、日本肉牛,终日无事可做,悠闲只等一死。它们不像西班牙的斗牛,全身精力。这就是中国的牛。