题目内容：

For ages, sailors have said that it is a good luck to see dolphins swimming alongside boats. Their presence meant that land is near, which will be vital informations if a boat and its crew are in danger. Some dolphins have even protected sailors which suffer shipwreck from sharks. There is no wonder that these unique and fascinating creatures have long known as our friends.

Dolphins are thought to be intelligent animals because of its quick ability to learn. They seem to communicate with each other through a combination of whistles and clicks. While scientists don’t know exact what they are talking about, it is thought that dolphins are telling each other that food is nearby, or warn each other of approaching dangerous.