单选题 The tomatoes your great-grandparents ate probably tasted little like the ones you eat today. In fact, tomatoes "were once so flavorful that you could take one in your hand and eat it straight away just like we regularly eat apples or peaches," according to plant scientist Alan Bennett. He belongs to a team of international scientists who now think they know one reason why the fruit has lost so much flavor.
Although some unripe tomatoes have a dark green patch near the stem, farmers prefer that their unripe tomatoes are the same shade of green all over. The consistent coloring makes it easier for them to know when the fruit should be picked.
But tomatoes without the dark green patch are also missing an important genetic ingredient that helps the fruit make more sugar and other tasty molecules. So by breeding tomatoes for that consistent color, Bennett's team says, crop scientists may have accidentally contributed to also making this fruit {{U}}bland{{/U}}. "It is a good illustration of unintended consequences," Harry Klee told Science News.
Tomatoes make sugars in compartments called chloroplasts (叶绿体). Bennett and his colleagues found that tomatoes need the correct version of a gene (one called S1GLK2) to form chloroplasts properly in the fruit. A gene acts as a biological instruction book that tells cells which molecules to make.
Tomatoes without the dark green patch have the wrong version of this gene, the researchers report in Science. As these fruits ripen, they can't make as many chloroplasts. And chloroplasts that they do produce are smaller. One result: The tomatoes make less sugar—and don't taste as good.
Tomatoes also produce gases responsible for some of the odors we associate with the fruit. Even though you only breathe them, these gases affect the way that you perceive flavor. Tomatoes with weak chloroplasts can't make as much of these gases, further reducing flavor.
But the newfound gene change is "not the whole story of why modern tomatoes are so bad, by a long shot," Klee told Science News. Tomatoes are also blander when they are picked too early or stored in the fridge.

单选题 Which of the following results from the help of crop scientists?

A. Tomatoes with various colors.
B. Improved color and taste of tomatoes.
C. Increased output of tomatoes.
D. Tomatoes with a consistent green color.

【正确答案】 D

【答案解析】第二段说有些未成熟的西红柿在靠近茎部的地方是深绿色，但是农民却希望它们变成统一的绿色，而不是有深有浅，认为这样会让他们更容易判断西红柿是否可以采摘了。第三段第二句说农学家就培育出了这种颜色均匀的西红柿。

单选题 The word "bland" (Para. 3) probably means ______.

A. less nutritious
B. less tasteful
C. more colorful
D. more productive

【正确答案】 B

【答案解析】第三段说这些西红柿茎部不再呈深绿色，但也因此缺少了能够产生更多糖分的基因成分。农学家培育出了这种颜色均匀的西红柿，也无意中造成了西红柿口感的平淡无味。bland的意思是“味道平淡的”。

单选题 What does Harry Klee think of the work of crop scientists?

A. It is a mixed blessing.
B. It is beneficial to farming.
C. It is hard to evaluate.
D. It does more good than harm.

【正确答案】 A

【答案解析】针对农学家培育出了这种颜色均匀的西红柿，但也无意中造成了西红柿口感的平淡无味，Harry Klee说：“这充分展示了无意带来的结果。”也就是说农学家并不是有意识地希望改变西红柿的味道，但改变了西红柿的颜色却无意中也改变了它的味道。改变颜色对于农民来说是件好事，但口感变差却又是件坏事，所以说是好坏参半。

单选题 What can be learned about chloroplasts?

A. The more the chloroplasts, the sweeter the tomatoes.
B. The smaller the chloroplasts, the better odor tomatoes have.
C. Chloroplasts help form the correct version of S1GLK2.
D. Chloroplasts mainly affect tomatoes' color, not their flavor.

【正确答案】 A

【答案解析】四至六段具体介绍了叶绿体的作用。第四段说西红柿需要正确的基因型来形成叶绿体。C选项的意思却是叶绿体帮助形成正确的基因型，所以是错误的。第五段说颜色一致的西红柿具有的是错误的基因型，无法产生足够多的叶绿体，而且产生的叶绿体也不够大。因此西红柿产生的糖分就少，味道也不够好。也就是说叶绿体越多越大，西红柿就越甜。所以答案是A。第六段说的是叶绿体和气味及口感的关系。叶绿体越少，西红柿的香味就越少。

单选题 Which of the following is NOT mentioned as a reason for tomatoes' flavor today?

A. The change of tomatoes' gene.
B. The time tomatoes are picked.
C. The soil where tomatoes are planted.
D. The storage temperature.

【正确答案】 C

【答案解析】第四至六段提到了基因改变对西红柿味道的影响。最后一段最后一句说如果采摘的过早或是储存在冰箱里，西红柿的味道也会变差。唯一没有提到的是C：种植西红柿的土壤。

单选题 The passage is mainly written to ______.

A. introduce the modern way of breeding tomatoes
B. compare tomatoes today and those in the past
C. describe how the tomato technology has evolved
D. explain why tomatoes today have lost much flavor

【正确答案】 D

【答案解析】