数据库管理系统常见的数据模型有层次模型、网状模型和______3种。

阅读理解。

     When Mencius (孟子) was a little boy, his father died. Mencius and his mother were quite poor. One day

Mencius returned home from school and found his mother making some cloth. It was very beautiful and

expensive.

      "How much of the book have you read today?" Mencius' mother asked him. "I haven't read any of it yet."

Mencius replied, "I played with some friends of mine in the fields." 

     When his mother heard this, she picked up a pair of scissors and cut the cloth. 

     "Why have you cut your cloth?" Mencius asked, "It was so beautiful but now you've wasted (浪费) it." "You

have wasted your time," his mother said, "now I have wasted mine. Look at the terrible things we have done."

     Mencius learnt a lot from this lesson. After that, he always studied hard.

1. When did this story happen? [ ]

A. Not long before liberation (解放).

B. More than 2000 years ago.

C. About 400 years ago.

D. In the 18th century.

2. What was Mencius doing while his mother was cutting the cloth? [ ]

A. He was reading his book.

B. He was playing in the fields.

C. He was trying to help her.

D. He was watching strangely.

3. The mother cut the cloth because _______. [ ]

A. she thought making cloth was wasting time

B. she wanted to give her son a lesson

C. she wanted to use more beautiful and expensive cloth

D. she wanted her son to do his lessons at once

4. Mencius and his mother were quite poor because ___________________.

5. When the mother knew Mencius had not read any books, she felt s__________________.

如果技术方案在经济上可行，则有（）。

A.财务净现值<0，财务内部收益率>基准收益率

B.财务净现值<0，财务内部收益率<基准收益率

C.财务净现值≥0，财务内部收益率≥基准收益率

D.财务净现值≥0，财务内部收益率<基准收益率

2011年10月1日，我国开始实施新的节能汽车补贴政策，以此刺激节能汽车的生产，减少汽车尾气排放。这样做[ ]

A．说明国家只重视节能减排工作

B．是国家加大节能减排力度的表现

C．有利于我国的可持续发展

D．有利于实现我国2020年减排目标

在其他条件相同的情况下，主动土压力E_a、静止土压力E₀和被动土压力E_p三者下列关系中（）项正确。

A．Ea≦E0≦Ep

B．Ea＜E0＜Ep

C．E0＜Ea＜Ep

D．E0≦Ea≦Ep

合同的撤销：是指因意思表示不真实，通过撤销权人行使撤销权，使已经生效的合同归于消灭。存在撤销原因的合同叫可撤销合同，这类合同多是因重大误解而成立的合同、因欺诈而成立的合同、因胁迫而成立的合同等。
　　以下属于可撤销的合同有( )。

A．甲、乙签订质押合同，约定甲不能如期履行合同义务，则乙取得质物的所有权

B．甲、乙两企业之间的资金借贷合同

C．甲为逃避法院的强制执行，将其财产赠与乙

D．甲因治病急需钱，乙提出以低于市场价接近5倍的价格购买甲的珍贵油画，甲无奈之下与乙签订了合同