题目

ID systems are used as a means for people to prove their identity, as a means of access control, or for many other situations. ID cards also contain a lot more information than simply the name of the holder. All ID cards contain information that is relevant to the institution that released them, so there is no single model that applies to all ID cards. Different institutions have different rules when it comes to ID cards, and ID cards used by students, in universities, will not have the same security features as those used in the military, for example. The more important the institutio16．在一段长3000米的公路两旁安装路灯（两端要安装），每相邻两根的距离是200米，一共需要安装多少盏路灯？