Apple rolled out new versions of its popular iPod music player. CEO Tim Cook also unveiled cheaper models of its Touch music player, a touchscreen-only device. An 8-gigabyte version now costs $229, down from $299. A 32-gigabyte model costs $399, down from $499. Suppose when the price of an iPod decreases by 20 percent, the number of songs downloaded on iTunes increases by 30 percent. Based on this information iTunes are
A. complements to iPods.
B. substitutes for iPods.
C. an inferior good.
D. a normal good.