The correct answer is B) It will lose its load and tend to overspeed. When an alternator loses its field excitation, it effectively becomes a generator that is no longer able to control its output voltage. Without field excitation, the alternator will lose its ability to regulate the voltage it produces, causing it to lose its load. This, in turn, will cause the alternator to tend to overspeed, as there is no longer a load on the generator to maintain its speed. The other options are incorrect because: A) The alternator will not become overloaded, as it has lost its load; C) The voltage will not remain the same, but will instead drop significantly; and D) The alternator will not supply excessive current to the bus, as it has lost its ability to generate power.