Notice! travellers intending to embark on the atlantic voyage are reminded that a state of war exists between germany and her allies and great britain and her allies; that the zone of war includes the waters adjacent to the british isles; that, in accordance with formal notice given by the imperial german government, vessels flying the flag of great britain, or any of her allies, are liable to destruction in those waters and that travellers sailing in the war zone on ships of great britain or her allies do so at their own risk.

what is the best summary of this message from the german government?

a. americans should declare their support for germany in the war.
b. americans who voice their support for britain will be at risk.
c. americans who sail across the atlantic on british ships are risking their lives.
d. americans who cross the atlantic risk starting a war with germany.