Context sensitive language is context free
This can be done in a similar way to the proof that it is undecidable whether the language of a context-free grammar is regular. A general statement of such undecidability properties is Greibach's theorem observed by  Sheila Greibach in 1968.


  Let $C$ be a family of languages effectively closed under union and
  concatenation with regular sets, and for which equality to $\Sigma^*$ is
  undecidable (for sufficiently large $\Sigma$). Let $P$ be a proper subset of $C$,
  which contains all regular languages, and is closed under single
  letter quotient. Then membership of $P$ is undecidable for $C$.


So, we have to check whether the context-sensitive and context-free languages meet the criteria of Greibach for $C$ and $P$.