Which of the following distinguishes earlier from later editions of the DSM?

A) Earlier editions didn't cover depression.
B) Later editions removed depression.
C) Later editions specify how long a person must exhibit symptoms to qualify for a diagnosis.
D) There are no significant differences between earlier and later editions.

Later editions of the DSM specify how long a person must exhibit symptoms to qualify for a diagnosis, while earlier editions did not have this requirement. The other options are incorrect as earlier editions did cover depression and it was not removed in later editions, and there are significant differences between earlier and later editions. Therefore, the best choice is C.