Final answer:
The sentence in question is in the passive voice because the action is performed on the subject rather than by the subject.
Step-by-step explanation:
The sentence 'In 1949, the U.S. Food and Drug Administration approved the first drug for the treatment of cancer: the chemical compound HN-2.' is in active voice. In active voice, the subject of the sentence acts. In this case, the subject 'the U.S. Food and Drug Administration' acts approving the drug. Passive voice would be if the sentence were written as 'The first drug for the treatment of cancer was approved by the U.S. Food and Drug Administration in 1949.'