Final answer:
The legal venue for testing nuclear weapons by nations today is restricted to underground due to the Partial Test Ban Treaty of 1963, although even these tests are limited by international law and treaties.
Step-by-step explanation:
In the modern world, the legal venues for a nation to test nuclear weapons are highly restricted due to international treaties and concerns about safety, environmental impact, and global security. The Partial Test Ban Treaty of 1963 prohibits nuclear weapons tests above ground, underwater, and in the atmosphere, limiting tests to underground environments to minimize nuclear fallout. However, even underground testing is subject to scrutiny, safety concerns, and political pressures because of its potential long-term environmental impacts and geopolitical ramifications.
Today, due to international agreements like the Nuclear Non-Proliferation Treaty and ongoing monitoring and efforts by the International Atomic Energy Agency (IAEA), testing nuclear weapons is generally discouraged and, in many cases, actively prevented on the global stage. Hence, the correct answer to the question is B. Below ground, with the understanding that even such tests are constrained by international law and should meet specific conditions and regulations.