The correct answer is C) all void spaces are filled. When loading bulk grain, it is important to ensure that all void spaces are completely filled to prevent the cargo from shifting during the voyage. Shifting cargo can create dangerous stability issues for the ship. Checking each cargo compartment after loading is a critical safety procedure to verify that no voids or air pockets have been left, which could allow the cargo to move unexpectedly. The other answer choices are incorrect because they do not directly relate to the key safety concern of preventing cargo shifting. Checking the cargo grade (A) and loading the heavier cargo in the lower hold (B) are also important, but do not address the specific issue of void spaces. Ensuring lighting circuits are energized (D) is a separate safety concern unrelated to the cargo loading process.