Using coordination:We didn't know his telephone number. We would have telephoned him.

【正确答案】正确答案：We would have telephoned him but we didn’t know his telephone number．

【答案解析】解析：译文：我们不知道他的电话号码。我们本来会给他打电话的。合并在一起意思为：我本来会给他打电话的，但是我不知道他的电话号码。两句为转折关系，所以可用并列连接词but连接。