Bill hаs been engаging in regulаr resistance training fоr оne year and fоllowing nutrition recommendations he learned about in his sports nutrition course. He has noticed that the improvements to his strength and weight gain have plateaued in recent months and he is seeking a recommendation from you regarding what nutritional supplement he could add to his diet to potentially overcome this plateau. Which of the following supplements is the best recommendation you can give to him based on the available evidence of the 4 answer choices.