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问题 单项选择题

“制定标准时要与国家有关法律相一致”体现了标准制定要求的

A.科学性 

B.准确性 

C.简明性 

D.统一性 

E.合法性

答案

参考答案：D

解析：

制定标准时应与法律法规相一致体现了制定标准统一的要求。

单项选择题

PET心肌显像的主要特点，下列错误的是（）

A.发射正电子核素，如11C、13N等

B.采用符合线路技术，使用机械准直，提高了探测效率

C.PET图像可以进行准确的定量分析，而SPECT只能进行定性或半定量分析

D.PET分辨率较高

E.PET较好地解决了组织重叠干扰心肌影像的问题
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单项选择题

Lichens may grow on the bark of a tree in a steaming tropical rain forest, on the bricks of big city buildings, on rocks in hot springs, on wind-swept mountaintops, and in the driest desserts. In the arctic, they provide the principal food for caribou, and they are one of the few plants that grow in Antarctica. They are pioneers, appearing in barren rocky areas and starting the formation of soil in which mosses, then ferns, and then other plants can take root.
Lichens are a partnership of two plants — fungi and algae. The lichen body is made up of a network of fungal strands. In the upper layers of these grow groups of algae. The two organisms live together to the benefit of both, a relationship known as symbiosis. The fungi provide support, absorb water, and shelter the tender algae from direct sunlight. The algae carry on photosynthesis and provide the fungi with food. The algae can live independently and are recognizable as a species that grows alone. The fungi, on the other hand, cannot live apart from their partners. They can be placed in known classes of fungi but are unlike any species that lives independently.
So definite are the form, color, and characteristics of these double organisms that for hundreds of years, they were classified as one. More than 15,000 "species" were named. If these organisms are classified as separate species, it is difficult to fit them into the existing system of classification. But if they are classified separately, these species of fungi seem rather strange. Lichens are a splendid example of the difficulties faced by taxonomists in classifying species.

Lichens may NOT grow ______ .

A．in the tropical woods

B．on the ceilings of city buildings
C．on rocks in hot springs

D．in dry desserts
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