The following multiple-choice is solved. Could you please explain to me why these are the results? I tried to calculate the first one, as an example but did not get the results until I did random operations that although gave the answers, I know are wrong. Could you please help me to state why these are correct? Thanks

17. If a company uses LIFO, which of the following would most explain a decrease in the gross profit margin or rate? (assuming Revenue remains constant) A) An increase in advertising expense B) A decrease in manufacturing costs C) An increase in competition D) Purchases of inventory at the end of the period E) All of the above would decrease Gross Profit. 18. Which of the following is an example of a cash flow from operating activities? A) Receipt of cash from lenders B) Payment of cash from the sale of common stock C) Payment of cash dividends to the stockholders D) Receipt of cash from customers E) Receipt of cash from the sale of a factory