冬天，河面结了一层较厚的冰，测得它能承受的最大压强为2.8×10⁴Pa.。小李的质量为60kg，每只脚的着地面积相同，均为250cm²，g=10N/kg，求：

①小李站在冰面上对冰面的压强为多大？

②为了能安全在冰面上行走，小李最多能背多少千克的物体？

    What do you know about the sea? Some people have seen it, but others haven't. The sea looks beautiful on a fine sunny day and it can be very rough when there is a strong wind. What other things do we know about it?

    Of course, the sea is very large. In the world there is more sea than land. If you swim in the sea, you know that the water is salty. Rivers take salt from the land into the sea. Some places of the sea are more salty than other places. Do you know the Dead Sea? Fish can't live in it!