题干

如图一表示某生态系统的食物网,甲~庚代表不同的生物.下列有关叙述中正确的是(    )

A:图一中的甲和庚分别属于第二,第三营养级

B:调查图一中的戊和庚的种群密度一般用标志重捕法

C:当丙刚迁入这个生态系统的一段时间内,数量变化如图二中的曲线X

D:若图二中的曲线Y代表的是该生态系统中丙的数量变化,则c点对应的是图三中的t1时刻,此时丙的出生率等于死亡率

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答案(点此获取答案解析)

C

同类题5

阅读下面短文,从短文后各题所给的A、B、C和D四个选项中,选出可以填入空白处的最佳选项。

    Medical bills were piling. Kids needed glasses, cars needed repairs and the dog needed surgery. On top of that, Christmas was almost 1 us so presents needed to be purchased.

    But all of that was 2 when my husband, Brian, was waiting in our local tire shop to have his six truck tires3 on a snowy night He overheard the tire salesman 4 a young mom with 3 children that she was in serious 5 of all new tires, as each one was completely 6 down.7, die young mom said she didn't have the money to replace more than one tire on her car.

    On hearing that, Brian 8 to pay for a tire to be installed,9of the one tire this woman was able to purchase. Brian knew that even though it was just a start, the young mom would be much 10 driving on the 11 roads with a balanced set of two new tires than they would with just one new tire.

    The young mom was so surprised that she 12 choked up. Eyes filled with tears, she thanked Brian and pulled away.

    My husband is a naturally modest13 man who feels rewarded in the giving, not m the 14 in life. So imagine his unexpected 15, when he later discovered the salesman had 16 the entire amount spent on the 17 tire to his bill!18 the seven tires my husband bought, the salesman only19 him for six.

    The simple act of one man making the decision to share what be had, rather than worrying about what he would 20, changed things that night.