If the piston is at TDC but not on the compression stroke, what position will the valves be in?

When the piston is at Top Dead Center (TDC) but not on the compression stroke, it indicates that the piston has reached its highest point, but it is likely on the exhaust stroke or the intake stroke contextually. In this scenario, it's possible for both valves to be slightly open due to the overlap phase in the engine's cycle.

During certain points in the four-stroke cycle, particularly between the closing of the exhaust valve and the opening of the intake valve, both valves can be slightly open to ensure smoother transitions. This overlap allows for efficient expulsion of exhaust gases and the intake of fresh air-fuel mixture, which optimizes performance and efficiency.

Thus, the correct understanding is that at TDC, the valve timing can be such that both valves could indeed be slightly open, which corresponds to the conditions described in the answer choice provided.