完成单位换算：1.2km= ____ m，15min= ____ s，36km/h= ____ m/s．
小明用弹簧测力计吊着一物块在空气中称时，读数为3N，当把物块浸没在煤油中称时，读数为2.5N，此时物块受到煤油的浮力为____ N。
Since our research so far has not produced any answers to this problem，we need to adopt a different________to doing it.
