A. Archimedes principle.
Archimedes' principle states that a body that is completely or partially submerged in a fluid is acted upon by an upward force, called buoyant force, the magnitude of which is equal to the weight of the fluid displaced.
From the principle, we can say that, if the weight of water displaced when the sip enters the water is at least equal to the weight of the ship, then the ship will float.
Thus the correct answer is option A.