a) are found only in the central nervous system
b) carry electrical signals along the length of an axon
c) are gaps between neurons where chemical signals are used to transmit information
d) allow electrical signal to jump between myelin segments

(c). are gaps between neurons where chemical signals are used to transmit information

Explanation:

Synapses can be defined as junction present between two nerve cells, through which nerve impulses are transmitted by using chemical signals or neurotransmitters. The synapses represent a small gaps that separate two neurons.

The neurotransmitters are released by ending of presynaptic neuron and allows transmission of signals from presynaptic neuron to postsynaptic neuron. Hence, synapses are necessary for unidirectional flow of impulses.

Thus, the correct answer is option (c).

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.