4.
The answer is: B
Explanation
For the first time ever, the ongoing joint Indo-US exercise has incorporated "Chemical, Biological, Radiological, and Nuclear (CBRN) terror response" in its training regimen. This reflects the recognition of chemical and biological warfare as a rising global threat.
The joint drill, named TARKASH, involves the participation of India's National Security Guard (NSG) and the US Special Operations Forces (SOF) and is being held in Chennai.