Final answer:
The rhetorical device used in the first sentence of Daniel Inouye's address is a metaphor, comparing the period of economic growth to a long journey. The correct answer is option: 2) metaphor.
Step-by-step explanation:
The first sentence of Daniel Inouye's Keynote Address at the Democratic National Convention uses a rhetorical device known as metaphor. This is identified by the phrase 'embarked on the longest unbroken journey of economic growth and prosperity,' which compares the historical period of economic growth to a long voyage without actually taking a sea journey.
The other options, like synecdoche, allusion, and alliteration, do not apply here. Synecdoche would involve a part representing the whole or vice versa, allusion would be a direct or indirect reference to another text or historical fact, and alliteration is a repetition of consonant sounds at the beginning of words.