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问题 选择题

相同物质的量浓度的下列物质的稀溶液中,pH最小的是(　　)。

A．乙醇

B．乙酸

C．氯化钠

D．碳酸

答案

答案：B

pH越小,酸性相对越强,乙酸、碳酸溶液呈酸性,乙酸酸性强于碳酸,乙醇、氯化钠溶液均为中性。

填空题

Last year I caught the baby cuckoo and put 56. ______
it in a cage outside. Later its mother flew from the cage 57. ______
with food in her mouth. I was happy to see this, because of 58. ______
the mother bird knew much better than I did to feed her 59. ______
baby. But the following morning I found the baby bird60. ______
died. I told the story of my bird to my biology teacher 61. ______
and he explained that what had happened. A mother 62. ______
cuckoo, finds her baby in a cage, will bring it poison63. ______
food. She believes it is good for her baby to die than to 64. ______
live in a cage. I still feel sorry for what I do to the bird.65. ______
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单项选择题

一般的螺纹连接都具有（），在静荷载和工作温度变化不大时，不会自行松脱。

A.自锁性

B.自闭性

C.固定性

D.稳定性
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