已知函数y=acos（2x+$\frac{\mathrm{\pi }}{3}$）+3，x∈0，$\frac{\mathrm{\pi }}{2}$的最大值为4，求实数a的值．

西周时期中国人形成了亲戚观念。父母，祖父母，叔伯、婶婶，姑姑是血缘关系中最近的亲人；外祖父母，舅舅、舅妈，姨妈是血缘关系第二重要的亲人。材料反映（    ）

经过60年的大规模建设和调整，我国产业层次不断升级，产业结构不断优化，产业关系趋向合理。1952年，我国三大产业的比重分别为51%、20.8%、28.2%，2011年我国三大产业的比重分别为10.6%、46.8%和42.6%，产业结构的现代化特征越来越明显。我国不断优化产业结构，有利于
①加快经济发展方式转变，促进资源合理配置  ②经济发展主要由依靠投资、出口拉动向依靠消费、投资、出口协调拉动转变③促进经济增长主要依靠第二产业带动向依靠第一、第二、第三产业协同带动转变④提高经济发展的质量和效益

下列四幅省区轮廓图中表示黑龙江省的是（　　）

根据短文内容回答问题。

    More and more children play computer games for a long time. Most parents feel quite worried about that. But in fact, not all games are bad for kids.

    There is a popular game called Mole Manor（摩尔庄园）on line now. In this game, it is a world of the kids. Children can do what they want to do there. They can buy what they want and even the pets. Almost every player has one or two pets called Lam. The players can buy something for Lam and they also want to give them some food to eat. Sometimes kids must wash their pets to keep them clean. At that time, they are the parents themselves. That helps them know how much their parents do for them. There are many other games for kids in Mole Manor. Kids can be a policeman here. They can also be a teacher to help the Lams to learn more.

    Get the kids to play for only half an hour on line. Don't hate all computer games and you can be a good parent.