短语讲解：

1. The United States ambassador to the United Nations is calling for a stronger international effort to stop the spread of the Ebola virus.

call for 要求
例句：Different circumstances call for different tactics. 
不同的情势需要不同的策略。 

2. More than 300 people were killed when the boat sank six months ago.

more than 多于
例句：There is more than a whiff of propaganda. 
所含之宣传实在不止一点点。 

3. They plan to ask for lesser sentences for the other 11 crew members.

ask for 请求…;  要求…
例句：He had the audacity to ask for an increase in salary. 
他竟然厚着脸皮要求增加薪水。