如图表示一交变电流的电流随时间而变化的图象，此交变电流的有效值为（  ）

 

    Many people like spring, because they can go out and do many kinds of activities. We made a survey about the activities that people like to do in spring. Here are the results.
Scott：
    In spring, I often visit my uncle and I like fishing with him. I also like boating and enjoy the beach. Last spring my uncle and I went boating. The dolphins came so close to us. It was very amazing. I hope that I can go there again soon.
Linda:
    My favorite spring activity is gardening (园艺). I think it is relaxing to work in the garden. I grow many flowers in my garden every year. They are so beautiful.
Nancy：
    I love spring. I love going to the beach and spending a whole day there. It is so relaxing to lie on the beach. I also like surfing in the sea.
James：
    I am twelve years old. My favorite spring activity is swimming. I started to learn swimming when I was seven years old. I always have a good time with my friends in the river.

如图是某农田长期使用一种农药后，害虫群体的密度变化曲线．下列分析不符合达尔文进化观点的是（　　）

某班50位学生期中考试数学成绩的频率分布直方图如图所示，其中成绩分组区间是：40，50），50，60），60，70），70，80），80，90），90，100．已知图中x=0.018，则由直观图估算出中位数（精确到0.1）的值为（    ）

在直角坐标系中，点M，N在同一个正比例函数图象上的是（　　）