题干

科研小组对某地两个种群的数量进行了多年的跟踪调查,并研究
N
t
+
1
N
t
随时间的变化趋势,结果如图所示(图中Nt表示第t年的种群数量,Nt+l表示第t+l年的种群数量).下列分析正确的是(    )

A:甲种群在0~t3段的年龄结构为增长型

B:乙种群在0~t1段的种群数量呈“J”型增长

C:乙种群在t2时数量最少

D:甲种群在t3后数量相对稳定可能是生存条件得到了改善

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答案(点此获取答案解析)

B

同类题3

通读下面短文, 掌握其大意, 然后在每小题所给的四个选项中, 选出一个最佳答案, 并将答题卡上对应的选项涂黑。

    My parents are busy with their work every day. You can't see there is love 1 them. They don't act in the romantic(浪漫的)2that I read in books or I see on TV.

    One day, while Mom was sewing(缝) a quilt,I 3 beside her. “Mom, I have a question,” I said after a while.

    “What?” she asked.

    “Is there love between you and Dad?” I asked her in a very low voice.

    She stopped sewing and 4 her head. Then she bowed her head and went on sewing.

    I thought I had hurt her. At last I heard my mother say, “Susan, look at this thread(线). Sometimes it appears, but most of it disappears in the quilt. It makes the quilt5. If life is a quilt, then love should be a thread. It can hardly be seen, but it's 6 there.”

    I couldn't understand her 7 the next spring. My father suddenly got sick. Mom had to stay with him in the hospital for a month.

    After they 8, my mother helped my father walk slowly down the country road every day. My father had never been so gentle.

    “Dad, how are you 9 now?” I asked him one day. “Susan, don't worry about me,” he said. “I just like walking with your Mom.”

     Once I thought 10 meant flowers, gifts and sweet kisses. But from this experience, I understand that it is just a thread in the quilt of our life . It is inside, making life strong and warm.