Answer: A. Chemical signal
Explanation:
Chemical signal is the type of communication which coordinates actions between neighboring cells
.
This ability originated in single cells organisms and was essential for the evolution of multicellular organisms because after a cell receives a message, it is transferred across the plasma membrane and changes are brought about within the cell in response to this message.
The slightest change in pH can destroy the substance or organism. The pH of a cell's interior helps regulate the cell's chemical reactions. For example, the pH of blood is 7.4, if blood falls to 6.8 or lower or 8.2 or higher, it results in death.
