We all know we have only one earth to live o__.It's our duty to p___ it.Everyone should do helpful
things for her.For e__,we must stop polluting the river and the lake.We should plant many trees and g___ to make our environment nice and clear.We plant trees to stop the the wind and the sand b___ towards the farmland.We should plant flowers to m___ our environment around us more beantiful.Please r___ we have one earth.We have one earth.We should protect her.She is our friend