そのスーツケースの一つは空っぽだ。

that (something or someone distant from the speaker, close to the listener; actions of the listener, or ideas expressed or understood by the listener); the; um...; er...; uh...

suitcase

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

one; for one thing; only; (not) even; just (e.g. "just try it")

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

empty; vacant; hollow

be; is; indicates past or completed action; indicates light imperative