Concept:The sentence has two words placed incorrectly, requiring a swap to fix grammar and meaning.
Explanation:The original sentence is: “A demanding boss expects their workers to efficiency at top levels … ensure perform.”
The word ‘efficiency’ (B) is a noun, but the structure “to ___” needs a verb.
The word ‘perform’ (D) is a verb, but the phrase “ensure ___” needs a noun.
So we interchange ‘efficiency’ (B) and ‘perform’ (D).
This change makes the sentence grammatically correct: “A demanding boss expects their workers to perform at top levels, though this very rarely happens when the boss themselves isn’t present to ensure efficiency.”
No other words need rearrangement.
Answer:D-B (Option 4)