Although the turtle has been toothless for more than 150 million years, in some contemporary turtle species the moderately sharp and jagged edges of their horny jaws function for teeth.
 | their horny jaws function for teeth |
| its horny jaws function for teeth |
| its horny jaws function as do teeth |
| the horny jaws function as teeth do |
| the horny jaws function as teeth 选E。说DO无法指虚词，但不知有什么更好的解释呢。 我只是觉得有DO语义表达更清楚。 |