Read the excerpt below from Moby-Dick by Herman Melville:
"For to go as a passenger you must needs have a purse, and a purse is but a rag unless you have something in it. Besides, passengers get sea-sick—grow quarrelsome—don't sleep of nights—do not enjoy themselves much, as a general thing..."
Considering the meanings conveyed by the vocabulary and grammatical structures employed in the passage, analyze the statements below and choose the alternative that best interprets the highlighted expressions within their context.

I.The modal verb must expresses necessity related to travelling as a passenger.
II.The word unless introduces a condition that affects the meaning of the previous statement.
III.The adjective quarrelsome describes a tendency to engage in arguments or disputes.
IV.The expression as a general thing indicates an exception to a commonly observed situation.


Which alternative presents the correct analysis?