搜题请搜索小程序“爱下问搜题”
问题 选择题

磷肥能促进作物根系发达，增强抗寒抗旱能力，下列物质中能用作磷肥的是[ ]

A．硫酸钾（K2SO4）

B．磷酸二氢钙Ca（H2PO4）2

C．尿素CO（NH2）2

D．白磷（P）

答案

答案：B

完形填空

阅读下面的短文，然后以约 30 个词概括故事的主要内容。

Who says honesty is dead? Last Tuesday morning Alan Reed, a student, was at the bank. He asked to take out $ 50 but the bank clerk mistakenly gave him five twenties instead of five tens. For a few seconds he wondered what to do. Should he give the extra money back? Keep it? If he kept it, he could buy several new books, or he could take his friend Alice to a fancy dinner. Probably no one would ever notice. Besides, this would make up for all the times he’d been overcharged. But then he looked at the clerk. She was a middle-aged woman with a sweet face, and she reminded him of his mother. She had been nice to him, and she looked pressured in her work. Then it occurred to him that the lady would probably get in trouble. Worst of all, Alan felt, he would probably feel guilty about keeping the extra cash. So Alan gave back the money.

The bank clerk was so impressed that someone was honest enough to return money not rightfully his that she contacted the newspaper. So there you have it. What would you have done if you’d been in Alan’s position?
查看答案
单项选择题

设有关系R（A，B，C），与SQL语句select distinct A from R where C=36等价的关系代数表达式是（）。

A．πA(σC=36(R))

B．σC=36(πA (R))

C．σC=36(πA,B (R))

D．πA,B(σC=36(R))
查看答案