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Plant Gas Scientists have been studying natural sources of methane (甲烷，沼气) for decades but hadn’t regarded plants as a producer, notes Frank Keppler, a geochemist(地球化学家) at the Max Planek Institute for Nuclear Physics in Heidelberg, Germany. Now Keppler and his colleagues find that plants, from grasses to trees, may also be sources of the greenhouse gas. This is really surprising, because most scientists assumed that methane production requires an oxygen-free environment. Previously, researchers had thought that it was impossible for plants to make significant amounts of the gas. They had assumed that microbes(微生物) need to be in environments without oxygen to produce methane. Methane is a greenhouse gas, like carbon dioxide. Gases such as me A. a oxygen-free environment B. an environment with the same concentration of oxygen as the Earth has C. a carbon dioxide-free environment D. an environment filled with the greenhouse gas [单项选择]男孩，2岁。1岁时患麻疹后食欲差。常有腹泻，身高83cm，体重7600g，面色苍白，皮肤干燥，腹部皮下脂肪0.3cm，心音低钝，脉搏缓慢。假设该患儿出现哭而少泪，眼球结膜有毕脱斑，则并发有（）
A. 维生素A缺乏 B. 维生素B2缺乏 C. 维生素C缺乏 D. 维生素D缺乏 E. 维生素E缺乏 [单选题]当某个业务单元的投资资本报酬率小于资本成本并且可持续增长率小于销售增长率时，应当优先采用的战略是()。
A.提高财务杠杆 B.分配剩余现金 C.出售该业务单元 D.降低资本成本 [判断题]高压设备停电时，工作人员可以单独移开或越过遮拦进行工作。
A.正确 B.错误 [简答题]启发式和注入式的根本区别是什么为什么我们要提倡启发式教学
[单选题]5 2 3
任何载流导体的周围都会产生磁场，其 磁场强弱与( )。 A.过导体的电流大小有关 B.导体的粗细有关 C.导体的材料性质有关 D.导体的空间位置有关 [单选题]开口于蝶筛隐窝的是
A.上颌窦 B.额窦 C.筛窦后小房 D.蝶窦 E.筛窦中小房 [单选题] 数字存储示波器的带宽最好是测试信号带宽的( )倍。
A.3 B.4 C.6 D.5 [单选题]铁路职业道德的基本原则是（）。
A.服务旅客 B.服务货主 C.认真工作 D.人民铁路为人民 我来回答: 提交
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