Which of the following best supports the idea that the melting of glaciers in antarctica is a global environmental threat?
a. the melting of glaciers can cause sea levels on earth to fall.
b. the melting of glaciers can change ecosystems in antarctica.
c. the melting of glaciers can harm animal populations in antarctica.
d. the melting of glaciers can cause coastal flooding on other continents.
i think it is a because it emphasizes that the whole earth will be affected, while c shows that it is an environmental threat.

I'm pretty sure there's a geometry rule for   anyways, if the triangle is equilateral, and the circle is circumscribed, the circle is outside of the triangle.  to find the area, you need the radius.  the radius should be a straight line from the center of the triangle to any of it's points.  draw lines from the center of the circle to each of the triangle points.  draw three more lines from the center to the middle of the sides of the triangle.  you should now have six separate 30-60-90 triangles inside of your original triangle. use your 30-60-90 rules to solve for the radius, then the circumference.