In the sentence below, select from the given options the phrase that should…

Concept: In traditional formal grammar (the register tested in competitive exams), the modal verbs shall and will split by person: with first-person subjects (I, we), shall is the standard form for a plain future action or a future consequence stated with certainty, while will expresses determination or promise. Should is the conditional/past form of shall and signals a hypothetical or an obligation, not a certain future outcome. Also, a double negative such as “not be unable” cancels out to an affirmative meaning.

Application: The sentence “Unless I get some break, I ___ do any more work” is a future-conditional statement: it states what will happen if the condition (getting a break) is not met. Since the subject is first person (I) and the result is a certain future consequence rather than a hypothesis, the modal must be shall, not should. The verb phrase must also stay a single negative, “not be able” — turning it into “not be unable” would wrongly assert ability. So the phrase that fixes both problems at once is “shall not be able”.

Cross-check: Substituting back — “Unless I get some break, I shall not be able to do any more work” — reads as a clear, grammatically sound future-conditional statement, matching the intended meaning that the speaker will be unable to continue working without rest.

Contrast — why each other option still fails:

• “should be unable”: keeps the incorrect modal “should” (a hypothetical/obligation sense, not a certain future), so the core modal-verb error is never fixed.

• “shall not be unable”: fixes the modal to “shall” but creates a double negative (“not…unable”), flipping the meaning to imply ability — the opposite of what the sentence needs.

• “should not be unable”: keeps the wrong modal “should” and also introduces the double negative, combining both errors.