The engineers had inspected the bridge several times without noticing the weakness. Only after a heavy truck crossed it ① did they detect an unusual vibration. Never before ② had the main support moved so visibly. Not until the traffic was stopped ③ they could examine the damaged joint. Rarely ④ had an inspection revealed such a narrow margin of safety. The team concluded that under no circumstances ⑤ should heavy vehicles use the bridge before repairs.
정답 ③① Only after로 제한 부사구가 문두에 와서 did they detect로 도치한 것이 적절하다.
② Never before가 문두에 있으므로 had와 주어의 도치가 적절하다.
③ 정답이다. Not until절 뒤 주절은 could they examine처럼 조동사와 주어를 도치해야 한다.
④ Rarely가 문두에 있어 had an inspection revealed로 도치한 것이 적절하다.
⑤ under no circumstances가 이끄는 부정 제한 표현 뒤에 should heavy vehicles use로 도치한 것이 적절하다.