begin{tabular*}{0.15textwidth}{@{extracolsep{fill}}{ | c |}}
  hline
  em { small {If transfer function,}} \
   hline
  em{ small {knows : The output or response can be expressed with various system to understand nature of systems. }} \
  hline
  em{ small {unknows : It may be found experimentally by studying with known  input and output of system.}}
  hline

end{tabular*}

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