正确答案: D

丁和甲中各元素质量比相同，则丁中一定含有-1价的元素

题目：甲、乙、丙、丁4中物质分别含2种或3种元素，它们的分子中各含18个电子。甲是气态氢化物，在水中分步电离出两种阴离子。下列推断合理的是

解析：D

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学习资料的答案和解析：

[单选题]The term “multitasking” originally referred to a computer’s ability to carry out several tasks at one time. For many people, multitasking has become a way of life and even a key to success. In fact, some excellent mental aerobic exercises (大脑训练) involve engaging the brain in two or more challenging activities at a time. Although checking e-mail while talking on a phone and reading the newspaper may be second nature for some people, many times multitasking can make us less productive, rather than more. And studies show that too much multitasking can lead to increased stress, anxiety and memory loss.In order to multitask, the brain uses an area known as the prefrontal cortex (前额叶脑皮层). Brian scans of volunteers performing multiple tasks together show that as they shift from task to task, this front part of the brain actually takes a moment of rest between tasks. You may have experienced a prefrontal cortex “moment of rest” yourself if you’ve ever dialed (拨电话) a phone number and suddenly forgotten who you dialed when the line is answered. What probably occurred is that between the dialing and the answering, your mind shifted to anther thought or task, and then took that “moment” to come back. Research has also shown that for many volunteers, job efficiency (效率) declines while multitasking, as compared to when they perform. only one task at a time.

To make them more productive.

解析：解析：推理判断题。根据第一段的内容可知，作者提出：“In fact, some excellent mental aerobic exercises (大脑训练) involve engaging the brain in two or more challenging activities at a time.”，之后用although引出转折，这种训练有时并不能productive。所以选择A。有部分人认为这种大脑的训练能够帮助他们高效的工作。

[单选题]萝卜主要的食用部位为次生木质部，胡萝卜主要的食用部位为次生韧皮部。( )

正确

[单选题]花药发育过程中，单核花粉(即小孢子)形成的过程是( )。

孢原细胞一造孢细胞一花粉母细胞一小孢子