Why are there increasing problems with construction in permafrost regions? a. the existence of black spruce trees b. global warming c. booming arctic populations d. longer freeze-thaw cycles

The correct answer is: B. Global warming.

The construction activities have much increased problems at the permafrost regions recently. The main reason for that is the climate change, or rather the global warming. Because the temperatures have increased, the permafrost is melted for certain parts of the year, while on others is slowly disappearing. That causes lot of movement and adjustment in the landscape. The previously constructed infrastructure has been damaged, on some places totally ruined. The permafrost is not stable anymore, thus the previous methods of construction are not suitable, so there's a very big problem when something needs to be constructed in this regions nowadays.

the thirteen colonies are:

connecticut, delaware, georgia, maryland, massachusetts, new jersey, new york, new hampshire, north carolina, pennsylvania, rhode island, south carolina, virginia

doctrine that the us had the right to expand throughout north america.