Which of the following is true according to the passage?
A.
When a patent becomes out of effect, it can be re-patented or extended if necessary.
B.
It is necessary for an inventor to apply for a patent before he makes his invention public.
C.
A patent holder must publicize the details of his invention when its legal period is over.
D.
One can get all the details of a patented invention from a library attached to the patent office.