The Best Means of Establishing the Proper Law for an International

The best means of establishing the proper law for an international contract is

A) to accept the same country where the contract would be submitted for arbitration.
B) for the parties themselves to make express provision.
C) for the parties to leave it by default to the country of signing.
D) for the parties to leave it up to the rules of the court of jurisdiction.
E) for the parties to make it subject to a "neutral" law.