A．The wolffish.　　 B．The harbor seal.

　　C．Human beings. D．The Atlantic cod.

　　C　[细节理解题。根据第二段中的"When it comes to predators，humans have to be placed first on the list..."可知，人类是龙虾生命的最大的威胁者。]

　　4．According to the text， can eat hard­shelled animals easily.

　　A．the Atlantic cod B．the summer flounder

　　C．the harbor seals D．the wolffish

　　D　[细节理解题。根据最后一段中的"These teeth are specifically for eating hard­shelled animals."可知选D项。]

　　B

　　The "swim­with­dolphins" tourist industry is becoming more popular every year. After all, it can cost a large amount of money to have this kind of holiday experience. So tour operators try to place eager swimmers as near as possible to the dolphins by trying to predict where the dolphins will be.

　　Research has shown that while dolphins can move away if they do not want to interact (交流) with human swimmers, they do not like it at all if the swimmers slip into the water directly on top of them or if humans are in their path of travel. However, if swimmers enter the water to one side of them, the dolphins do not avoid the swimmers to the same extent.

　　In all cases, the dolphins seem to have become more sensitive to the presence of the swimmers. For dolphins, swimming amongst or with humans is not necessarily a high priority. This study has shown that only 19% of any group of dolphins will participate in interaction. Young dolphins are the most likely to interact. It is believed that they see humans as "entertainment" and that the interaction is a new and unusual experience for them.

It is frequently asked whether "swim­with­dolphins" tourism should be discontinued. The advice is that dolphins should be given enough periods of time throughout the day when they are not exposed to tourism. Permitted interactions should not be too disturbing to the dolphins since there could be mothers and calves (幼崽) present in dolphin groups. There should also be educational campaigns about the