(a) General rule.--A person is not guilty of an offense unless his liability is based on conduct which includes a voluntary act or the omission to perform an act of which he is physically capable.
(b) Omission as basis of liability.--Liability for the commission of an offense may not be based on an omission unaccompanied by action unless:
(1) the omission is expressly made sufficient by the law defining the offense; or
(2) a duty to perform the omitted act is otherwise imposed by law.
(c) Possession as an act.--Possession is an act, within the meaning of this section, if the possessor knowingly procured or received the thing possessed or was aware of his control thereof for a sufficient period to have been able to terminate his possession.