What structure most directly stimulates a skeletal muscle fiber to contract?

The right answer is motor neuron.

A motor neuron is a nerve cell that is directly connected to a muscle and controls its contraction. Motor neurons are the exit route from the central nervous system or the final route of any motor act. The cellular bodies of the motor neurons are located either in the brainstem or in the ventral horn of the gray matter of the spinal cord.

Hi again :)

Sorry I couldnt help ya yesterday but Im going to try and help you now

Balanced equation for this is

CH4 + 202 > c02+ 2h20

The law of conservation of mass states that after a reaction the mass stays the same.

It has to obey because everything does or it is improper

Using Avogadro MOLES formula one mole is 6.02 x 10^23

(Im sorry I cant draw a mole table on here)

You have to work out the mass from the moles

We know that mass = Mr  x moles

Using this formula we can calculate the atomic number and Mr

There is one mole so the mass numbers correspond accordingly