Bollworms are a traditional threat to cotton crops．Young ones feed on the boll,

Bollworms are a traditional threat tocotton crops．Youngones feed on the boll, the part of the

cotton plant that contains the seeds．

A bacterium known as Bt is able to killbollworms and some other pests．Bt is short form for Bacillus thuringiensis．It was discovered in the earlytwentieth century．Farmersbegan using Bt as a natural pesticide（杀虫剂）．

Then，in the 1990s，researchers found a way to grow cotton plants that contain a Bt gene．The genetically modified cottonplant produces toxins that kill bollworms．Farmers around the world are now growing an estimated fourteenmillion hectares of Bt cotton．

Cotton bollworms also attack other crops．But scientists in Chinarecently reported that Bt cotton may help suppress bollworm in other cropsgrowing nearby．

The study involved crops grown in sixprovinces of northern China between 1992 and 2008.The study area containedthree million hectares of cotton and twenty-two million hectares of corn，peanuts，soybeans and vegetables．

The researchers say the study suggestedthat Bt cotton not only controls bollworm on the transgenic cotton，but also may reduce itspresence on other crops．And that reduction，they say，may decrease the need for insecticide use in general．

But the researchers also pointed outconcerns．They saybollworms could develop resistance to the cotton plants designed to resist them．And they noted that insectscalled mirids have become “key pests” of cotton in China．They said this is because of a decrease in pesticide use madepossible by Bt cotton．

The researchers say they do not believethat Bt cotton alone can solve all insect problems．Instead，they say farmers in Chinashould consider it just one part of pest management systems．

44．What is Bt in this passage?

         A．It's a kind of hi-techinvention．      B．It's a natural bacterium．

         C．It's a kind of pest．                   D．It's a man-made pesticide．

45．Bt cotton has all the advantages EXCEPT that ________．

         A．it resists bollworms

         B．it does good to other cropsgrowing around

         C．it reduces the use ofinsecticide

         D．it helps to develop new insects

46．The underlined word “ones” inthe first paragraph refers to ________．

         A．bollworms            B．cotton crops          C．cottonseeds        D．pests

47．From the passage，we can infer ________．

         A．farmers around the world arenow growing a large area of Bt cotton

         B．researchers are probably nowsearching for new ways to solve other cotton problems

         C．bollworms could not exist in Btcotton any longer

         D．Chinese scientists found theway to grow Bt cotton

试题答案

【答案】

 B

 D

 A

 B

【解析】