Which sentence best describes how art in buddhist cave temples along the silk road reflects the beliefs of the chinese people?

a. the cave temples were built to be sheltering places for revered emperors when they traveled from town to town.
b. the cave temples served as houses for the crews who built the great wall of china.
c. the cave temples were built to store silk and porcelain, which the chinese valued above all other goods.
d. the cave temples were built as religious shrines and retreats for travelers and monks.