Either b or d im not for sure which one it is but its one of them
The nitrogen cycle provides nitrogen to the ecosystem from the atmosphere, ground and oceans. Nitrogen is an important component of complex molecules such as amino acids and nucleotides, which lead to the creation of proteins and DNA, the building blocks of all life .
C. it is the small opening in the center of the eye
The answer is B, it is the only answer that talks about electric signals.