Select all the correct answers.
Henry collects shells from the beach every day he is on vacation. Each day he collects shells, he always collects three times as many white shells as black shells. Which of these ratio statements could compare the number of white shells to black shells Henry collects in one day?
a. For every 12 white shells, there are 4 black shells.
b. For every 15 white shells, there are 3 black shells.
c. For every 26 white shells, there are 8 black shells.
d. For every 27 white shells, there are 9 black shells.
e. For every 21 white shells, there are 7 black shells.