Об­ра­зуй­те от слова REAL од­но­ко­рен­ное слово так, чтобы оно грам­ма­ти­че­ски и лек­си­че­ски со­от­вет­ство­ва­ло со­дер­жа­нию тек­ста.

A recent study may have an answer to one of the greatest unsolved mysteries in science  — what is the purpose of sleep? The work suggests it’s ______ about making animals function more efficiently in their environments.