B

Climbing Mount Everest, the world’s highest mountain, has now become more difficult. The government of Nepal asks climbers to come down the mountain with at least 18 pounds of garbage. That’s the average amount of garbage a climber leaves behind on Mount Everest.

Climbers would leave garbage along the way. This helps climbers keep their bags light, so they would have energy to reach the summit. The garbage problem in Mount Everest is not new. In 2013, climbers carried down a total of four tons of garbage.

The new rule came into effect in April of 2014. To make sure it is followed, climbers will have to hand in some money to the officials before they climb the mountain. When they climb back down the mountain, the officials will check them to make sure they bring down the 18 pounds of garbage. If they do, their money will be given back to them. If not, climbers won’t get their money back. Also, the officials won’t let these people climb the mountain again.

食品安全应考虑的问题包括（    ）

①食物本身是否有毒，②食品的保质期，③食物含能量高低，④是否被农药等有毒物质污染，⑤维生素种类，⑥无机盐含量，⑦食物的营养价值，⑧食物是否发霉变质

“秦王扫六合，虎视何雄哉！”李白诗中赞颂的“秦皇”是我国历史上著名的千古一帝秦始皇。能够成就他千古一帝业绩的史实是（    ）

①灭六国，建立中央集权国家 ②统一文字、货币、度量衡 ③修筑万里长城，防御匈奴 ④分科考试，选拔官吏

实验室有一瓶无色无毒气体，如图所示．请你用学过的知识对该气体做出一种假设（猜想），并按你的假设进行探究，填写下表．

若代数式﹣2a³b^m与3aⁿ⁺¹b⁴是同类项，则mn=____．