问题 单项选择题

转基因作物同普通植物的区别只是多了能使它产生额外特性的基因.早在1983年,生物学家就已经知道怎样通过生物工程技术将外来基因移植到某种植物的脱氧核糖核酸中去,以便使它产生靠杂交方式根本无法获得的某种新的特性:抗除莠剂的特性、抗植物病毒的特性、抗某种害虫的特性等.用以移植的基因可来自任何生命体:细菌、病毒、昆虫等.转基因作物目前在世界上已种植有1 000万公顷左右,种植最多的是棉花、玉米和西红柿等.在实验室试种的还有莴笋、西瓜、稻谷等品种.试验的目的除了增产之外,还在于提高这种品种的抗病毒能力.但同时也有专家担心转基因作物可能对环境有危险.比如在美国种植的那种能抗虫害的玉米和棉花,可能加快出现一更难对付的害虫.这类作物的所有分子都分泌出一微量的“杀虫”一种像任何一种一样能选择杀死某害虫的“雾剂”.尤其是那些能抗除莠剂的作物,它们一旦同野生状态下的“表姐妹”杂交之后,那些“表姐妹"也就会因此而成为除莠剂无法除掉的变种了对于这种技术,尽管还有些问题需要继续研究,但这确是人类9000年作物栽培史上一场空前的革命.

下列说法符合原文意思的一项是______.

A.转基因作物的研究已取得突破性进展,目前所有品种都得到推广种植

B.提高作物抗病毒的能力仍然是转基因技术研究没有完全解决的问题

C.更难对付的害虫的加快出现将是转基因作物给环境带来的最大的危险

D.增产并不是转基因技术研究的目的,提高抗病毒能力是研究者最感兴趣的

答案

参考答案:B

解析:依照文中“转基因作物目前在世界上已种植有1000万公顷左右”可判断出A项错误;依照文中“试验的目的除了增产之外,还在于提高这种品种的抗病毒能力.”可判断出D项错误.关于C项,文中并未提出有关于环境的问题.所以,B项正确.

单项选择题 B型题
单项选择题

Electronic mail has become an extremely important and popular means of communication.

The convenience and efficiency of electronic mail are threatened by the extremely rapid growth in the volume of unsolicited commercial electronic mail. Unsolicited commercial electronic mail is currently estimated to account for over half of all electronic mall traffic, up from an estimated 7 percent in 2001, and the volume continues to rise. Most of these messages are fraudulent or deceptive in one or more respects.

The receipt of unsolicited commercial electronic mail may result in costs to recipients who cannot refuse to accept such mail and who incur costs for the storage of such mail, or for the time spent accessing, reviewing, and discarding such mail, or for both. The receipt of a large number of unwanted messages also decreases the convenience of electronic mall and creates a risk that wanted electronic mail messages, both commercial and noncommercial, will be lost, overlooked, or discarded amidst the larger volume of unwanted messages, thus reducing the reliability and usefulness of electronic mail to the recipient. Some commercial electronic mail contains material that many recipients may consider vulgar or pornographic in nature.

The growth in unsolicited commercial electronic mail imposes significant monetary costs on providers of Internet access services, businesses, and educational and nonprofit institutions that carry and receive such mail, as there is a finite volume of mail that such providers, businesses, and institutions can handle without further investment in infrastructure. Many senders of unsolicited commercial electronic mail purposefully disguise the source of such mall.

Many senders of unsolicited commercial electronic mall purposefully include misleading information in the messages’ subject lines in order to induce the recipients to view the messages. While some senders of commercial electronic mail messages provide simple and reliable ways for recipients to reject (or ’opt-out’ of) receipt of commercial electronic mall from such senders in the future, other senders provide no such ’opt-out’ mechanism, or refuse to honor the requests of recipients not to receive electronic mail from such senders in the future, or both.

Many senders of bulk unsolicited commercial electronic mail use computer programs to gather large numbers of electronic mail addresses on an automated basis from Internet websites or online services where users must post their addresses in order to make full use of the website or service.

The problems associated with the rapid growth and abuse of unsolicited commercial electronic mall cannot be solved by the government alone. The development and adoption of techno-logical approaches and the pursuit of cooperative efforts with other countries will be necessary as well.

"Disguise" in Paragraph 4 is closest in meaning to ().

A. reveal

B. hide

C. deliver

D. post