题干

科学家在对黄化豌豆幼苗切段的实验研究中发现,切段内一定浓度的生长素会促进细胞的伸长,当生长素浓度达到一定值后就会促进乙烯的合成,而乙烯含量的增高,反过来又抑制了生长素促进切段细胞的伸长作用。以下观点符合上述例子的是(  )

A:不同浓度生长素的作用有差异,但都起促进作用

B:激素调节在植物的生长发育过程中发挥着重要作用

C:乙烯的主要作用是促进果实成熟

D:生长素和乙烯在植物的生长中表现为协同作用

上一题 下一题 0.0难度 选择题 更新时间:2016-12-29 02:19:21

答案(点此获取答案解析)

B

同类题5

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项,并在答题卡上将该项涂黑。选项中有两项为多余选项。

        America's holiday shopping season started on Black Friday, the day after Thanksgiving.

____Shoppers make the most money this time of year, about 20 percent to 30 percent of all revenue all year. About 136 million people shopped during the Thanksgiving Holiday weekend.

____In an era of instant information, shoppers can use their mobile phones to find deals. Nearly 80 percent of this year's holiday shoppers, or about 183.8 million people, shopped on Cyber Monday.____Online spending on Black Friday rose 15 percent to hit $2.7 billion this year. Cyber Monday spending increased 12 percent to $3 billion. NBC News reported that for many, shopping online was a more comfortable alternative than crowded malls.

      The shift to online shopping has had a big impact on solid shopping malls. Since 2010, more than 24 shopping malls have closed and anadditional 60 are struggling. Fortune says the weakest of the malls have closed. However, the business in malls is thriving again, it adds.  According to a survey, 94.2percent of malls were full with shops by the end of 2014.____

      The average American consumer will spend about $805 on gifts. That's about $630.5 billion between November and December – an increase of 3.7percent from last year.

____That goes toChina's Singles' Day, celebrated on November 11, which posted record sales of$14.3 billion in 2015.

A.More and morepeople shop online nowadays.

B.That is thehighest level in 27 years.

C.It is thebusiest shopping day of the year.

D.One-in-fiveAmericans used a tablet or smart-phone.

E.Thetraditional mall industry can hardly survive.

F.Cyber Mondayfalls on the Monday after Thanksgiving and Black Friday.

G.Nonetheless,Cyber Monday is not the biggest online shopping day in the world.