题目

It may seem like a moment in a science fiction movie. In a fierce battle, a creature loses an arm but, then, grows another one to take its place. However, this is not science fiction. It is scientific fact. Some fish and amphibians, such as salamanders, can regrow lost limbs and organs. As mammals evolved they lost the ability to regrow, or regenerate, parts of their body. However, experiments show that it may be possible to regain that ability. Tropical freshwater zebrafish are popular pets. They are also popular as lab animals. Their embryos(胚胎) are clear, or translucent. They ca 脱式计算．47×3+254     371×6-206 104×5×3     413-130+325．