What is garbage collection in the context of Java?

$1$ point

$($a$)$ The operating system periodically deletes all the java files available on the system.

$($b$)$ Any package imported in a program and not used is automatically deleted.

$($c$)$ When all references to an object are gone, the memory used by the object is automatically reclaimed.

$($d$)$ The JVM checks the output of any Java program and deletes anything that doesn$$t make sense.

$($e$)$ Janitors working for Sun Micro Systems are required to throw away any Microsoft documentation found in the employees$$ offices.