A radio message from the mainland had been received by the ship's captain instructing him to give up the search.

问题：

1.后面是动名词引导的从句吗？是否可以补充完整为which was instructing him to give up the search。

【答】

1. 动名词引导的从句——该说法不正确。

2. instructing him to give up the search，是现在分词短语作定语，修饰a radio message。中间隔着had been received by the ship's captain。这种现象叫做“词语分隔（定语和被修饰语被谓语所分隔）”。又如：

The problem arose of what to do with the money.

The time is coming to prepare for Christmas.

3. 可以变成定语从句：which was instructing him to give up the search，但稍嫌啰嗦，不如现在分词简练。

2. 此句能否改为：A radio message from the mainland which (that) had been received by the ship's captain instructed him to give up the search.

【答】这样变化后，语法不错。但意思与原句出现不一致。原句的中心意思是“无线电报被船长收到”，改后的句子是“无线电报指示船长放弃研究”。