阅读下列短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项，并在答题卡上将该项涂黑。
A
At first, the earth’s surface layer (层 ) was made up of huge blocks of hard, solid rocks.There slowly, the rocks broke up into smaller and smaller pieces. Finally stones, pebble(卵石) and grains of sand were formed. Many sorts of plants and animals lived and died on the surface of the earth. Their remain mixed up with the stones, pebbles and formed soil. The outmost layer of the earth is soil.
