甲、乙两种物质的相对分子质量分别为M和N．若将甲、乙两种物质的溶液混合，当溶液中甲与乙的质量比为2M：N时，充分反应后溶液的pH=7，则甲和乙应是下列物质中的（　　）

科学家所取得发明创造的成就与他们从小____科学、善于观察与思考，能够____问题和____问题的答案，及追求真理、献身科学的精神有关。

如图是一个平面直角坐标系，按要求完成下列各小题．

    Mr Jones and Mr Brown work in the same office. One day Mr Jones says to Mr Brown, “We want to  have a small party at our house next Wednesday evening. Do you and your wife want to come ?”

    Mr Brown says, “Thank you very much. I must phone my wife and ask her.” So Mr Brown goes to the other room and makes a telephone call. When he comes back, he isn't happy.

    “Why are you not happy?” asks Mr Jones, “Do you speak to your wife?”

    “No, She isn't at home. My little son answers the phone. He says she is looking for him outside(在外面) .”