题目

Do you know about DNA? Here is an introduction of it.DNA is short for deoxyribonucleic acid. It contains genetic instructions. These instructions are used in the development and functioning of all known living organisms(有机体). That's to say that your DNA decides what you are like. Perhaps this is a little bit difficult for you to understand. Here is an example to explain it more clearly. Before you were born, your DNA had already decided you would have two hands and that each hand would have five fingers. Your_hands_would_help_you_hold_things_and_do_many_other_things.However, DNA is more 已知一个三角形的三边长为3、8、a，则a的取值范围是_____________．