Hydrogen gas is harmless to your feet so since you don’t need protection against it that seems the best answer.
Valleys are one of the most common landforms on the Earth and they are formed through erosion or the gradual wearing down of the land by wind and water. In river valleys for example, the river acts as an erosional agent by grinding down the rock or soil and creating a valley
Newton's 3 laws are...
inertia: things tend to continue to do what they are doing.
Change: to make something change you need a force to change it. the force needed = the mass times its acceleration
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Resistance: When you push on something, it pushes back.
From yahoo answers
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