(2)"T his allows them to dive to a depth of over 2000 feet"中的this就是指前一句的内容"A seal can go for 40 minutes without a breath". (3)由"Seals are well designed to swim in water"可知。 (4)最后一段说“海象与海豹的不同之处在于海象体形更 大,长着大大的牙齿"(Walruses differ...
seal1 (sēl) n. 1. a.A device or material that is used to close off or fasten an opening or connection, especially to prevent the escape of a liquid or gas:used caulk as a seal around the window. b.An airtight closure:a door that lacks a tight seal. ...
Mammalia is a ‘class’. A class is one of the groups that zoologists use to classify animals. The groups have a hierarchy (which means levels of importance). A ‘kingdom’ is the top level; all animals are members of the animal kingdom, just as all plants are members of the plant ...
seal1 (sēl) n. 1. a.A device or material that is used to close off or fasten an opening or connection, especially to prevent the escape of a liquid or gas:used caulk as a seal around the window. b.An airtight closure:a door that lacks a tight seal. ...