\begin{dependency}
\begin{deptext}
CH$_4$ \& + \& 2O$_2$ \& --->  \& CO$_2$ \& + \& 2H$_2$0 \\
\end{deptext}
\depedge{1}{5}{
1C}
\depedge{1}{7}{
4H}
%\depedge{4}{3}{advmod}
%\depedge{4}{5}{xcomp}
%\depedge{5}{6}{dobj}
\end{dependency}


\begin{dependency}
\begin{deptext}
CH$_4$ \& + \& 2O$_2$ \& --->  \& CO$_2$ \& + \& 2H$_2$0 \\
 (16g) \& + \& (64g) \& --->  \& (44g) \& + \& (36g) \\
\end{deptext}
\end{dependency}

\begin{dependency}
\begin{deptext}
CH$_4$ \& + \& 2O$_2$ \& --->  \& CO$_2$ \& + \& 2H$_2$0 \\ \\
 (16g) \& + \& (64g) \& --->  \& (44g) \& + \& (36g) \\
\end{deptext}
\wordgroup{1}{1}{7}{a}
\wordgroup{3}{1}{3}{a0}
\wordgroup{3}{5}{7}{a1}
\groupedge[edge below]{a0}{a1}{80g}{4ex}
\end{dependency}

\begin{dependency}[theme=brazil]
\begin{deptext}
CH$_4$ \& + \& 2O$_2$ \& --->  \& CO$_2$ \& + \& 2H$_2$0 \\ \\
 (16g) \& + \& (64g) \& --->  \& (44g) \& + \& (36g) \\
\end{deptext}
\wordgroup{1}{1}{7}{a}
\wordgroup{3}{1}{3}{a0}
\wordgroup{3}{5}{7}{a1}
\groupedge[edge below]{a0}{a1}{80g}{4ex}
\end{dependency}

\begin{dependency}[theme=iron, label theme=copper]
\begin{deptext}
CH$_4$ \& + \& 2O$_2$ \& --->  \& CO$_2$ \& + \& 2H$_2$0 \\ \\
 (16g) \& + \& (64g) \& --->  \& (44g) \& + \& (36g) \\
\end{deptext}
\wordgroup{1}{1}{7}{a}
\wordgroup{3}{1}{3}{a0}
\wordgroup{3}{5}{7}{a1}
\groupedge[edge below]{a0}{a1}{80g}{4ex}
\end{dependency}

\begin{dependency}[label style = {circle}]
\begin{deptext}
CH$_4$ \& + \& 2O$_2$ \& --->  \& CO$_2$ \& + \& 2H$_2$0 \\ \\
 (16g) \& + \& (64g) \& --->  \& (44g) \& + \& (36g) \\
\end{deptext}
\wordgroup{1}{1}{7}{a}
\wordgroup{3}{1}{3}{a0}
\wordgroup{3}{5}{7}{a1}
\groupedge[edge below]{a0}{a1}{80g}{4ex}
\end{dependency}