The correct answer is C) With arm extended downwards and forefinger pointing down, move hand in small horizontal circles. This hand signal is the standard way to indicate to the crane operator that they should lower the load. The extended arm and downward pointing finger clearly communicates the desired direction of movement, while the small horizontal circular motion provides the "lower" instruction. The other options are incorrect because they do not directly and unambiguously signal the crane operator to lower the load. Option A could be interpreted as a "stop" signal, while options B and D do not specify the downward direction.