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【Paragraph 7】One potential problem is that opening the mouth to breathe detracts from the streamlining of these　fishes and tends to slow them down. Some species of tuna have specialized grooves in their tongue. It is thought that　these grooves help to channel water through the mouth and out the gill slits, thereby reducing water resistance.　(Swimming Machines)

　　Which of the sentences below best expresses the essential information in the highlighted sentence in the　passage? Incorrect answer choices change the meaning in important ways or leave out essential information.

　　○These fishes often have a problem opening their mouths while swimming.

　　○The streamlining of these fishes prevents them from slowing down.

　　○The streamlining of these fishes tends to slow down their breathing.

　　○Opening the mouth to breathe can reduce the speed of these fishes.