The data in the following table show the total income spent on goods A, B, C, D of a household. Assume that the price of goods does not change.
\begin{tabular}{|l|l|l|l|}
\hline Spending/Income & Unit & \begin{tabular}{l}
First year \\
\( (100 \) million VND)
\end{tabular} & \begin{tabular}{l}
Second year \\
\( (200 \) million VND \( ) \)
\end{tabular} \\
\hline Goods A & Million VND & 30 & 50 \\
\hline Goods B & Million VND & 30 & 70 \\
\hline Goods C & Million VND & 25 & 20 \\
\hline Goods D & Million VND & 15 & 60 \\
\hline
\end{tabular}
1. What is the income elasticity of demand for each good?
2. Classify the goods A, B, C, D? Why?
