In TypeScript, what does the warning "this implicitly has an 'any' type because it does not have a type annotation" indicate?
A) The variable this is not declared in the current scope.
B) The type of this is not explicitly specified, so it is assumed to be of type any, which may lead to type safety issues.
C) The type of this is automatically inferred as string based on its usage.
D) The code is missing a required function return type annotation.