Which is used to determine earthquake risk a. changes in the color of rocks near faults b. hydrogen gas emissions near fractures c. the height of ocean waves d. strain in rocks near faults

The option (b) ''Hydrogen gas emissions near fractures'' is the correct option.

Explanation:

Hydrogen gas is highly mobile and insoluble in the earth's water. It causes the mechanical changes in the crustal rocks due to its high mobility nature.  

When it flows into the water, it reacts with water and forms hydrogen peroxide. The outflow of the charges causes electric current in the earth's crust. If it will continue emitting charges then it will cause EM pulses which will lead to the earthquake

the answer would be the third option, "no, ariel should have added 9^2 and 12^2 and compared that to 15^2."

this is found through the pythagorean theorem, which is a^2 + b^2 = c^2.

this is the correct way of solving the problem:

9^2 + 12^2 = 15^2

81 + 144 = 225

225 = 225