正确答案: D

无染色体，只能在DNA水平产生可遗传变异

题目：与酵母菌相比，硝化细菌具有的特点是________

解析：解析：本题考查真核生物与原核生物的区别及微生物相关知识，考查学生的理解能力。酵母菌为真核生物，硝化细菌为原核生物，硝化细菌无线粒体，但是需氧型生物，进行有氧呼吸，A错。硝化细菌无固氮酶，但能利用无机氮NH3作氮源，B错。硝化细菌无细胞核，但进行分裂生殖，不能进行出芽生殖，C错。硝化细菌为原核生物，无染色体，所以只能在DNA水平产生可遗传变异,D正确

查看原题

举一反三的答案和解析：

[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]Children who are not active or ___diet is high in fat will gain weight quickly.

whose

[单选题]

presented

[单选题]若复数z1=1+i，z2=3-i，则z1·z2=（ ）

4+2 i

解析：

【答案】A

[单选题]Amy joined a painting group but didn’t seem to _______, so she left.

fit in

[单选题]ESunday is more like Monday than it used to be, Places of business that used to keep daytime “business hours” are now open late into the night. And on the Internet, the hour of the day and the day of the week have become irrelevant (不相关的).A half century ago in the United States, most people experienced strong and precise dividing lines between days of rest and days of work, school time and summer time. Today the boundaries still exist, but they seem not clear.

the line between work time and rest time is unclear

[单选题]．2009年网络热词“躲猫猫”“钓鱼执法”“被增长”“被就业”等大部分来自于社会热点事件，彰显着中国公民意识的增强。这说明（ ）

社会意识是社会存在的反映 B．社会意识具有相对独立性

[单选题]人参药用部分主要是( )。

A和B

[单选题]_______, she is the sort of woman to spread sunshine to people through her smile.

lighthearted and optimistic