题干

研究生态系统的能量流动,可以参考如下模型:下列有关叙述正确的是    

A:研究生态系统中的能量流动,一般在群体营养级水平上

B:研究能量流经某一种群的能量时,要考虑到能量被利用和未被利用等方面

C:模型中的“能量输入”就是指捕食者的捕食

D:模型中的“能量散失”指呼吸作用散失的能量

上一题 下一题 0.0难度 选择题 更新时间:2013-04-09 06:27:48

答案(点此获取答案解析)

D

同类题5

根据短文内容,从短文后的七个选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

    The holiday season isn't about shopping and gifts.____ However, holiday travel can be more expensive than gifts. Fortunately, the following tips will help keep your travel spending under control.

    Plan ahead. The earlier you book your travel, from airfare to hotels, the easier it is to find good deals.____ Your best prices on airfare come when you book three weeks before the plane leaves for domestic(国内的) flights. For international flights, consider booking 30 days in advance. Many experts point out that you should book travel between one month and three months out for high-traffic holidays.

    Book your air travel on cheaper days. Traveling by air on Tuesdays and Wednesdays often costs less than on Fridays and Sundays. During the holidays, it's not just about a specific day of the week. You also need to consider the days surrounding the holiday but days immediately before and after a holiday can be expensive. One of the best ways to save is to plan your air travel on the day of the holiday.____

    Consider traveling overnight. Red-eye flights and overnight flights often cost less than those at more convenient times.____  Traveling overnight can help you avoid a night in the hotel, as well as save your money on travel to your destination.

    ____ You can't bring liquids with you on the airline, but you can bring sandwiches and other snacks. When you're on the road, you can buy food at local groceries to make your own meals, especially if you have access to(可使用) a microwave.

A. Bring your own food.

B. Consider affordable accommodations.

C. Traveling by plane is not the best choice.

D. Plus, booking earlier can save your money.

E. For instance, traveling on Christmas Day might be a great deal.

F. A great deal of travel also takes place during this time of year.

G. Other choices include sleeper trains as well as overnight ferries.