The correct answer is B. disastrous.
A catastrophic defeat is a very bad defeat, one that is likely to have serious consequences. It is often used to describe a military defeat, but it can also be used to describe a defeat in any other field, such as politics, business, or sports.
The word "improbable" means unlikely to happen. It would not be accurate to describe a catastrophic defeat as improbable, because it is a very real possibility in any competitive situation.
The word "revolutionary" means causing or relating to a radical change. It would not be accurate to describe a catastrophic defeat as revolutionary, because it is not a change that is likely to lead to a fundamental change in the way things are done.
The word "pessimistic" means expecting the worst to happen. It would not be accurate to describe a catastrophic defeat as pessimistic, because it is not a defeat that is necessarily expected to happen.
In conclusion, the correct answer is B. disastrous.
