Step 1: Count cis/trans isomers for \(\mathrm{C_5H_{10}}\).
The alkenes are:
\[
\mathrm{Pent\mbox{-}1\mbox{-}ene}
\]
(no geometrical isomer),
\[
\mathrm{Pent\mbox{-}2\mbox{-}ene}
\]
(gives cis and trans),
\[
\mathrm{2\mbox{-}Methylbut\mbox{-}1\mbox{-}ene}
\]
(no geometrical isomer),
\[
\mathrm{3\mbox{-}Methylbut\mbox{-}1\mbox{-}ene}
\]
(no geometrical isomer),
\[
\mathrm{2\mbox{-}Methylbut\mbox{-}2\mbox{-}ene}
\]
(no geometrical isomer).
Hence,
\[
\boxed{2}
\]
cis/trans isomers are possible.
Step 2: Count cis/trans isomers for \(\mathrm{C_4H_8}\).
Among the alkenes,
\[
\mathrm{But\mbox{-}2\mbox{-}ene}
\]
exists as
\[
\boxed{\text{cis and trans}.}
\]
All other alkenes do not exhibit geometrical isomerism.
Hence,
\[
\boxed{2}
\]
cis/trans isomers are possible.
Therefore,
\[
\boxed{2,\ 2}
\]
Hence,
\[
\boxed{(D)}
\]
is the correct answer.