The plumber was unable to finish the difficult job in one day. = The plumber couldn't finish the difficult job in one day. The plumber [subject] was unable [verb - periphrastic modal with meaning of modal can] to finish [infinitive object] the difficult job [object complement] in one day [infinitive object adverbial phrase] What did the plumber do? [He was unable to finish ...] To finish what? [the difficult job] To finish when? [in one day]

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