What is the name of the system of measurement used by most countries around the world?
A. British system
B. Scientific system
C. Systeme Internationale (SI)
O D. Measurement system

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.

d) a person who learns about the world by observing it.

explanation:

scientist are people who discover why and how things are done and made in the world.