1.______ it took only 70 days to complete the merger was a source of amazement to all

those concerned, especially in light of the difficulties surrounding the organization

of the company.

1.that             2.what

3.then             4.to



빈칸에 들어갈 게 4번 to 빼놓고는 다 될거 같은데 정답은 that 이라고 나왔네요

3.then 을 쓰면 \'그리고 70일이 걸렸다~\'식으로 문장이 성립되지 않나요?

왜 1번이 답인지...