It stands for "alcohol clinical training" when including alcohol, although that is not the most common usage of the acronym. More commonly it would stand for "american college testing".
...of strict social stratification...
The focusing of conscious awareness on a particular stimulus, as in the cocktail party effect (ability to attend selectively to only one voice among many). thats the answer
A short term environment change would be drought, smog, volcanic eruptions, and blizzards. All because it only last for a small period of time and it can affect the way certain species will have to adapt to certain environments.
