From a heavy gun that was raised, the captain realized that theship must have been a cruiser. In another chest, which contained the belongings of aship's officer, there was an unfinished letter which had been written on March 14th, 1943. The captain learnt from the letter that the name of the lost ship was the Karen.

　　13. From a heavy gun that was raised, the captain realized that the ship must havebeen a cruiser.

　　从捞起的一门大炮来看，船长认为那艘船一定是艘巡洋舰。

　　语言点:句子结构分析:that was raised是定语从句，修饰gun。后面分句中的that引导宾语从句，交代realised的内容。注意，must have been不表示对现在情况的推测，而是对过去情况的推测。

　　14. In another chest, which contained the belongings of a ship's officer, there was anunfinished letter which had been written on March 14th, 1943.

　　另一只海底沉箱中装的是船上一位军官的财物，其中有一封写于1943年3月14日的信，但没有写完。

　　语言点:句子结构分析:第一个which引导非限制性定语从句，修饰chest。第二个which引导定语从句，修饰letter。

　　15. The captain learnt from the letter that the name of the lost ship was the Karen.

　　从这封信中船长了解到沉船船名是“卡伦”号。

　　语言点:句子结构分析:这句话的主体结构是“learn from…+宾语从句”。