The target population is all stocks in the S&P 500 index. Is each of the following a parameter or a statistic? (a) The average price/earnings ratio for all 500 stocks in the S&P index. (b) The proportion of all stocks in the S&P 500 index that had negative earnings last year. (c) The proportion of energy-related stocks in a random sample of 50 stocks. (d) The average rate of return for 20 stocks recommended by a broker