Answer : The correct answer is " System ".
A group of things or part that form a whole is known as system .
Or System can be defined as a interacting or interdependent group of items that is forming a unified whole . For example : Gravitational system , thermodynamic system . These both systems have interacting bodies which influenced by some force .
Or it can be said : A group of parts that are combined to form whole which works a complete unit . For example : computers , telephones etc .