39 Why is it so hard to examine the powers and limits of the human brain?
(A)The hard facts of life cannot be measured.
(B)The inner secrets of the brain have not been revealed yet.
(C)The drive to test the human brain has been encouraged.
(D)Complex calibrations are prompted.

What makes people smart? It is a question that scientists and philosophers哲學家 have thought about for centuries, prompting complex calibrations標準校正, from head measurements to brain-ending彎 tests.

Yet the drive to probe追問；探究 the powers—and the limits—of the human mind has been thwarted挫敗 by the hard facts of life：the brain was virtually幾乎；實際上 a black box, its inner secrets locked within.

Now, scientists are using the latest technology to peer仔細看，端詳 inside. Using machines such as the PET scanner and FMRI machines, which map the changes in the brain’s blood flow, researchers at U.C. Irvine and elsewhere在別處 are producing the first images of how gifted有天才的，有天賦的, 聰慧 and not-so-gifted, minds go about the task of thinking.

In one study, Professor Richard Haier of U.C. Irvine found that brighter people have lower metabolic代謝 rate probably because their brains are more efficient.

However, when bright people are given harder tasks, their brains work harder than the average person’s.

Apparently, brain activity depends, to some extent面積，範圍, on the difficulty level of the task and the level of effort required.