问题 选择题

在正方体ABCDABCD′中,过对角线BD′的一个平面交AA′于E,交CC′于F,则以下结论中错误的是(   )

A.四边形BFDE一定是平行四边形

B.四边形BFDE有可能是正方形

C.四边形BFDE有可能是菱形

D.四边形BFDE在底面投影一定是正方形

答案

答案:B

解:如图:

①由平面BCB′C′∥平面ADA1D1,并且B、E、F、D′四点共面,

∴ED′∥BF,同理可证,FD′∥EB,故四边形BFD1E一定是平行四边形,故①正确;

②若BFD′E是正方形,有ED′⊥BE,这个与A′D′⊥BE矛盾,故②错误;

③由图得,四边形BFDE有可能是菱形,故③正确;

④当点E和F分别是对应边的中点时,平面BFD′E⊥平面BB1D′,故④正确.

故答案为B

阅读理解

It is Sunday today. Ann is shopping with her mother. She wants her mother to buy a new sweater for her. In a clothing shop, she finds an orange one. She tries it on (试穿). It is too small. She wants a bigger one, but the bigger ones are not orange. Ann doesn’t like other colours. Her mother asks:” Shall we go to another shop to have a look? ” So they go out of the shop and go into another one.

The second shop is bigger than the first, and in it there are many kinds of sweaters of different sizes and colours. Ann tries on an orange one. It is too big. She tries a smaller one. It is OK.

“How much is it ?” Ann’s mother asks the women who sells clothes. Then they find it too dear (贵), and they don’t have so much money with them.

“Would you like a cheaper one ? ” The women asks.

“ No, we shall take this one. My daughter likes it. We will come back to buy it tomorrow. ” Ann’s mother answers.

小题1: It is Sunday. Ann and her mother                

A.are at home

B. are in a clothing shop

C.are in a restaurant

D. are in a park小题2: Ann wants to buy          .

A.an orange

B.an orange sweater

C.an orange for her mother

D.an orange sweater for her mother小题3:There is only one             .

A.shop near her home

B.orange in the first shop

C.orange sweater in the first shop

D.orange sweater in the second shop小题4: The orange sweater in the first shop is          .

A.too small

B.OK.

C.longer

D.too dear.小题5:In the second shop, why don’t they buy the sweater ?

A.Because Ann doesn’t like the sweater.

B.Because it’s too small.

C.Because they don’t have enough(足够的) money.

D.Because they want to buy a cheaper one.

填空题