documentclass{report}
usepackage{tabularx}
usepackage{lipsum}
usepackage{multirow}
renewcommand{tabularxcolumn}[1]{m{#1}}
begin{document}
begin{tabularx}{0.5linewidth}{llX}
  multirow{2}{*}{A} & B & lipsum[1][1-2] \
                     & C & lipsum[2][1-3]\
end{tabularx}
end{document}

documentclass{report}
usepackage{tabularx}
usepackage{lipsum}
usepackage{multirow}
begin{document}
% with X as p-column 5 works:
begin{tabularx}{0.5linewidth}{llX}
  multirow{5}{*}{A} & B & lipsum[1][1-2] \
                     & C & lipsum[2][1-3]\
end{tabularx}

%X as m-column:
renewcommand{tabularxcolumn}[1]{m{#1}}
begin{tabularx}{0.5linewidth}{llX}
  multirow{1}{*}{A} & B & lipsum[1][1-2] \
                     & C & lipsum[2][1-3]\
end{tabularx}
end{document}

documentclass{report}
usepackage{tabularx}
usepackage{lipsum}
usepackage{multirow}
renewcommand{tabularxcolumn}[1]{m{#1}}
begin{document}
begin{tabularx}{0.5linewidth}{llX}
  multirow{9}{*}{A} & B & lipsum[1][1-2] \
                     & C & lipsum[2][1-3]\
end{tabularx}
end{document}

documentclass{report}
usepackage{tabularx}
usepackage{array}
usepackage{lipsum}
begin{document}
noindentbegin{tabular}{|ll}
hline
  A &
    begin{tabular}{@{}lm{.352linewidth}@{}}
        B & lipsum[1][1-2]\
        C & lipsum[2][1-3]\
    end{tabular}\
    hline
end{tabular}

vspace{4ex}noindentbegin{tabularx}{.5linewidth}{|llX}
    hline
    A & B & Just for benchmark\
    hline
end{tabularx}
end{document}