The correct answer for this question is (A) Groups of cells form tissues.
In multicellular animals, a group of similar cells alongwith inter-cellular substances perform a specific function. Such an organization is called tissue. All complex animals consist of only four basic type of tissues. These tissues are organized in specific proportion and pattern to form an organ like stomach, lung, heart and kidney. When two or more organs perform a common function by their physical and/or chemical interaction , they together form organ system, eg., digestive system, respiratory system, etc. Cells, tissues, organs and organ system split up the work in a way that exhibits division of labour and contribute to the survival of the body as whole.
They need to replicate themselves to make sure they don't get smaller.
Differentiation is the best process basically.
