The limited test ban treaty forbids nuclear testing in every area but
aboveground
outer space
underwater
underground

The correct option is: "aboveground"

The Comprehensive Nuclear-Test-Ban Treaty is an international treaty, signed for the first time on September 10, 1996, which prohibits the conduct of nuclear tests in and by the signatory countries.

The treaty was opened for signature in New York on September 24, 1996, when it was signed by 71 states, including five of the eight with nuclear capacity. Currently, the CTBT has been signed by 178 countries out of a total of 195, and ratified by 144. On January 16, 2007 ratification of the treaty was completed by all European countries, with the ratification of Moldova.

i confess that there are several parts of this constitution which i do not at present approve, but i am not sure i shall never approve them: for having lived long, i have experienced many instances of being obliged by better information or fuller consideration, to change opinions even on important subjects, which i once thought right, but found to be otherwise. it is therefore that the older i grow, the more apt i am to doubt my own judgment, and to pay more respect to the judgment of others.