课时作业26
ⅰ.阅读理解
a
(2013•辽宁卷)here is an astonishing and significant fact:mental work alone can't make us tired.it sounds absurd.but a few years ago,scientists tried to find out how long the human brain could labor without reaching a stage of fatigue(疲劳).to the amazement of these scientists,they discovered that blood passing through the brain,when it is active,shows no fatigue at all!if we took a drop of blood from a day laborer,we would find it full of fati