can someone explain to me why this is correct in like simple terms

Which of the following best describes diversification? A) The correlation coefficient between a completely diversified portfolio and the market portfolio is equal to 1 because a diversified portfolio carries only market risk. B) As the number of assets in a portfolio increases, the amount of systematic risk decreases because of diversification. C) You cannot achieve any diversification by combining two assets whose correlation coefficient is zero. D) Diversification reduces the variability of returns (as measured by the standard deviation) of each individual stock held in a portfolio. E) None of the above