2011年6月4日，位于智利首都圣地亚哥以南的普耶韦火山群持续喷出高热烟灰及石块，大量火山灰及石块冲上云霄．结合材料，回答题．

下列反应中，起了氮的固定作用的是

党的十八大报告首次提出并系统论述了社会主义协商民主制度，这是报告的一大亮点。这一制度下，将通过国家政权机关、政协组织、党派团体等渠道，就经济社会发展重大问题和和涉及群众切身利益的实际问题广泛协商，广纳群言、广集民智，增进共识、增强合力。健全这一制度
①有助于扩大公民参与政治生活的权利
②有助于党和国家决策的科学化、民主化
③有助于改进党的领导方式和执政方式
④有助于体现我国社会主义民主政治的特色和优势

阅读理解

    Most Chinese eat three meals a day. In the past,they had breakfast in the morning, a big lunch at noon, and a light supper at night.

    But now both men and women in the big cities have to work on the weekdays. So they often eat bread, eggs, milk and porridge forbreakfast at home. For lunch, Chinese take-away food is very popular. They often have a quick lunch in their workplaces.

    After work in the afternoon, they have more time for supper. They usually eat a big meal at home. Wives often cook meat, fish, chicken, vegetables and rice for their family.You can also find dumplings and noodles on the table in most families of northern(北方的)China.

下列关于减数分裂的叙述，正确的是 高考资源网
①减数分裂包括两次连续的细胞分裂②在次级精母细胞中存在同源染色体③着丝点在第一次分裂后期一分为二④减数分裂的结果是染色体数减半，DNA数不变⑤同源染色体分离，导致染色体数目减半⑥联会后染色体复制，形成四分体⑦染色体数目减半发生在第二次分裂的末期。