在“一带一路”建设中，政府实施积极的财政政策，可以购买服务，增加对道路、桥梁、口岸、码头等公共工程的投入；政府也可以购买规划，比如跨境道路的设计等，从而使“一带一路”成为我国经济发展的增长点。实施积极的财政政策，有利于（  ）

①减少投资需求，稳定经济增长           

②扩大信贷规模，稳定货币币值

③调整经济结构，优化资源配置           

④扩大投资需求，促进经济增长

设a、b∈R，那么ab＝0的充要条件是(　　)

   Mr. George works at the school lost and found. He works very carefully. Every day, when he gets a lost thing, he takes notes about it. There are pens, books, school uniforms, keys, walkmans and many other things in the lost and found. Most of them are the students’. If you lose your things, it’s easy for you to go to the lost and found for help. But you must tell Mr. George what it is and its color and the day when you can’t find it. I think Mr. George is very helpful, and you will be happy when you find the lost there.