Common explosives include the following, except:

The correct answer is C, anthrax, because it is not classified as an explosive. Instead, anthrax is a serious infectious disease caused by the bacterium Bacillus anthracis, typically affecting livestock and can be transmitted to humans. It is primarily recognized as a biological agent, rather than an explosive material.

On the other hand, Composit-4, ANFO, and Semtex are all established types of explosives used in various applications. Composit-4 is a plastic explosive typically used for demolition and military purposes. ANFO, which stands for Ammonium Nitrate Fuel Oil, is a widely used bulk explosive in the mining and construction industries due to its effectiveness and relative safety. Semtex is another plastic explosive known for its versatility and is often employed by military and special operations units. Thus, while the other options are associated with explosive materials, anthrax stands out as a biological threat, reinforcing why it is the exception in this context.