Calculate the gross profit percentages for each of the following situations and, based on these results, identify which situations are most preferable:

a. Sales of $450,000, cost of goods sold of $300,000

b. Sales of $660,000, gross profit of $230,000

c. Sales of $700,000, gross profit of $330,000

d. Sales of $800,000, gross profit ratio of 25% E-967