Prove that for each $n > 0,$ a language $B_{n}$ exists where
- $B_{n}$ is recognizable by an $\text{NFA}$ that has $n$ states, and
- if $B_{n} = A_{1}\cup...\cup A_{k},$ for regular languages $A_{i},$ then at least one of the $A_{i}$ requires a $\text{DFA}$ with exponentially many states$.$