Messages are sent to the brain or spinal cord from the body via neurons; messages leave the brain and spinal cord via neurons.

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds

sound moves fastest in solids because the molecules are tightly packed and it allows sound to vibrate