In the narwhal the single unicorn-like tusk is a modified upper tooth, whereas the paired tusks of the beaked whales are modified lower teeth.是什么意思_In the narwhal the single unicorn-like tusk is a modified upper tooth, whereas the paired tusks of the beaked whales are modified lower teeth.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句