first :you rent the house ,they have to charge the money for house living,water and electricity using every one month not two months ,not 15 days.(你必须每个月交一次房租，水电费)。 second ：many students have been shanghai, not only him.(我们班很多同学都去过上海)。 third ：before three o'clock we can arrive at the destination at the present rate . I am not sure that you can understand my Interpretation or not ,thank you .