"We've been working on this problem for over 10 years and the vaccines we've tried in the past have induced some immune responses but they have not been very effective."
The difficulty of the college entrance examination is the recruitment exam, there is no certain it will be difficult to have the selection effect, so the test is usually hard to.
The answer to this riddle lies in the metabolic activity of early photosynthetic life-forms that slowly but surely transformed the chemical composition of Earth's atmosphere.
This striking difference must have some effect and, because the difference is in the parts of the brain involved in intellect, we should be looking for differences in intellectual processing.