When a large number of species is lost over a relatively short time span,such as a few centuries,this situation is described as: 

A)  an eco-catastrophe 
B)  an extinction spasm 
C)  a major death sequence 
D)  an extinction sink

An extinction spasm refers to the rapid loss of a large number of species over a relatively short time span, often caused by human activities such as habitat destruction, pollution, and climate change. This term is commonly used by scientists to describe ongoing mass extinctions. Option A is too vague and does not specifically refer to the loss of species. Option C is not commonly used in scientific literature. Option D refers to a location where extinction rates are particularly high, rather than a specific event.