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9投标人的投标文件是否有效？对其撤回投标文件的行为应如何处理？

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从优势视角看，丽芬拥有哪些资源？

Why Is it So Difficult to Swat a Fly？
The brains of flies are wired to avoid the swatter, US researchers said on Thursday.
At the mere hint of a threat, the insects adjust their preflight stance to flee in the opposite direction, ensuring a clean getaway, they said in a finding that helps explain why flies can so easily evade swipes from their human foes.
"These movements are made very rapidly, within about 200 milliseconds, but within that time the animal determines where the threat is coming and activates a set of movements to position its legs and wings," Michael Dickinson of the California Institute of Technology said in a statement.
"This illustrates how rapidly the fly's brain can process sensory information into an appropriate motor response," said Dickinson, whose research appears in the journal Current Biology.
Dickinson's team studies this process in fruit flies using high-speed digital imaging equipment and a fancy fly swatter.
In response to a threat from the front, the fly moves its middle legs forward, leans back and raises its back legs for a backward takeoff. If the threat is from the side, the fly leans the other way before takeoff.
The findings offer new insight into the nervous system of the fly, and lends a few clues on how to outsmart them.
Dickinson, a bioengineer, has devoted his life's work to the study of insect flight. He has built a tiny robotic fly called Robofly and a 3-D visual flight simulator called Fly-O-Vision.

意志行动过程可分为、两个阶段。

人自觉地确定目的，有意识地根据目的，调节支配行动去克服困难，从而实现目的的心理过程叫做______。