[Tex/LaTex] subequations align

Question

Can anyone help me fix this problem?
Actually, there is no need to have 1(b), 1(d), 1(f) and 1(h) since they are deriving from the last line. Can I have just four subequations?

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{subequations}
\begin{alignat}{4}
E_{11}&=Q_{11}^2\ln\sqrt{B'_{11}} +Q_{12}^2\ln\sqrt{B'_{22}}+Q_{13}^2\ln\sqrt{B'_{33}}\\
&=Q_{11}^2\ln\sqrt{B'_{11}}+Q_{21}^2\ln\sqrt{B'_{33}}\\
E_{12}&=Q_{11}Q_{21}\ln\sqrt{B'_{11}}     +Q_{12}Q_{22}\ln\sqrt{B'_{22}}+Q_{13}Q_{23}\ln\sqrt{B'_{33}} \\
&=Q_{11}Q_{21}\ln\sqrt{B'_{11}}-Q_{11}Q_{21}\ln\sqrt{B'_{33}}\\
E_{22}&=Q_{21}^2\ln\sqrt{B'_{11}} +Q_{22}^2\ln\sqrt{B'_{22}}+Q_{23}^2\ln\sqrt{B'_{33}}\\
&=Q_{21}^2\ln\sqrt{B'_{11}} +Q_{11}^2\ln\sqrt{B'_{33}}\\
E_{33}&=Q_{31}^2\ln\sqrt{B'_{11}} +Q_{32}^2\ln\sqrt{B'_{22}}+Q_{33}^2\ln\sqrt{B'_{33}}\\
&=Q_{32}^2\ln\sqrt{B'_{22}}
\end{alignat}
\label{straincomponent}
\end{subequations}

\end{document}

Answer 1

another variation, with the equation number for each pair positioned vertically between the two lines:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{subequations}
\begin{align}
\begin{split}
E_{11}&=Q_{11}^2\ln\sqrt{B'_{11}} +Q_{12}^2\ln\sqrt{B'_{22}}+Q_{13}^2\ln\sqrt{B'_{33}}\\
&=Q_{11}^2\ln\sqrt{B'_{11}}+Q_{21}^2\ln\sqrt{B'_{33}}
\end{split}\\
\begin{split}
E_{12}&=Q_{11}Q_{21}\ln\sqrt{B'_{11}}     +Q_{12}Q_{22}\ln\sqrt{B'_{22}}+Q_{13}Q_{23}\ln\sqrt{B'_{33}} \\
&=Q_{11}Q_{21}\ln\sqrt{B'_{11}}-Q_{11}Q_{21}\ln\sqrt{B'_{33}}
\end{split}\\
\begin{split}
E_{22}&=Q_{21}^2\ln\sqrt{B'_{11}} +Q_{22}^2\ln\sqrt{B'_{22}}+Q_{23}^2\ln\sqrt{B'_{33}}\\
&=Q_{21}^2\ln\sqrt{B'_{11}} +Q_{11}^2\ln\sqrt{B'_{33}}
\end{split}\\
\begin{split}
E_{33}&=Q_{31}^2\ln\sqrt{B'_{11}} +Q_{32}^2\ln\sqrt{B'_{22}}+Q_{33}^2\ln\sqrt{B'_{33}}\\
&=Q_{32}^2\ln\sqrt{B'_{22}}
\end{split}
\end{align}
\label{straincomponent}
\end{subequations}
\end{document}