The correct answer is C) slightly greater than the bus frequency. When paralleling two AC generators, the incoming generator's frequency should be slightly greater than the bus frequency in order to ensure a smooth and seamless connection. This allows the incoming generator to naturally synchronize with the bus and prevents large circulating currents that could damage the equipment. Setting the incoming generator's frequency slightly higher than the bus ensures that the generator's voltage is leading the bus voltage, allowing for a smooth closing of the breaker and stable parallel operation. The other options are incorrect because: A) a frequency slightly less than the bus would result in the generator lagging the bus and potential damaging circulating currents, B) exactly equal frequency may not provide enough lead to reliably close the breaker, and D) a frequency more than 5 Hz higher could cause excessive generator loading and instability when the breaker is closed.