Air pollution is the presence of harmful substances in the earth's what?

Suggest why placing wheels under a heavy box reduces the neccessary force required to push it along at a constant speed.

As the pea seeds respire, the level of coloured liquid in the left hand part of the capillary tube rises. by referring to what is happening in the apparatus, explain why the level of liquid changes

Natural resources are any materials that humans obtain from the earth to meet our wants and needs.