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問答題

創(chuàng)建數(shù)據(jù)表時(shí)，可以不用定義主鍵（）

A.正確
B．錯(cuò)誤

答案： B．錯(cuò)誤在創(chuàng)建數(shù)據(jù)表時(shí)，主鍵（Primary Key）是用來唯一標(biāo)識(shí)表中每一行記錄的一個(gè)或一組字段。主鍵的定義不是強(qiáng)制性...

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請(qǐng)?jiān)诘赺_（49）__處填上正確答案。查看材料
A.In Belgium， when you buy something in a plastic or glass container， you make a deposit.
B.This is because too much padding can give buyers a false impression of what they are buying.
C.This has resulted in a 74 percent reduction in sales.
D.Tesco said it was saving 112，000 tons of cardboard a year by switching to reusable plasticcrates （裝貨箱） for transporting its fresh produce.
E.The campaign was initiated by The Independent newspaper.
F.If a product is over-packaged， don"t buy it.

A.In
B.
B.This
C.
C.This
D.
D.Tesco
E.
E.The
F.
F.If
G.

二氧化碳滅火器使用后干凈無污染。特別適用于油脂和電器起火，但不能用于撲滅金屬著火（）

A.正確
B．錯(cuò)誤

答案： B．錯(cuò)誤二氧化碳滅火器雖然適用于撲滅油脂和電器火災(zāi)，因?yàn)樗鼈儾粫?huì)留下殘留物，不會(huì)導(dǎo)電，且不會(huì)對(duì)電器設(shè)備造成損害。然而，二...

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