题目

阅读下面材料，根据其内容和所给段落开头续写两段，使之构成一篇完整的短文。Yesterday a heat wave hitthe town. It's too hot! Let's go for a swim after we finish our chores (家务活) at home! Joseph complained to his little brother, Loren.As the boys walked toward the Little Colorado River, they saw Sam and Frank,who ran to join them. Swimming's just what we need to cool off! Samsaid, kicking a rock.Sure it is,Frank agreed. Then he looked at the field they were passing. There were manyround watermelons in Farmer Davis's patch (小块地). Hey, Joseph Frank sai一定温度下，在一定容的密闭容器中充入N2和H2发生如下反应：N2+3H22NH3，并达到平衡，此时N2的转化率为c%，向平衡混合物中再次充入N2，重新达到平衡后N2转化率将（    ） A．增大       B．减小        C．不变         D．无法确定