Answer the Question on the Basis of the Following Five $\quad$

Answer the question on the basis of the following five schedules,all of which represent income tax schedules for an economy.All figures are in billions of dollars. $\quad$ $\quad$ $\quad$ $\quad$ I $\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$ II $\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$ III $\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$ IV $\quad$$\quad$$\quad$$\quad$$\quad$$\quad$$\quad$ V
$\begin{array}{c}\begin{array}{c}\\\underline{\text { Tax} } \\ \$ 30 \\50 \\60 \\70\end{array}\begin{array}{c}\text { Base } \\\underline{\text { (Income) }}\\\$ 100 \\200 \\300 \\400\end{array}\begin{array}{c}\\\underline{\text { Tax } }\\ \$ 10 \\20 \\30 \\40\end{array}\begin{array}{c}\text { Base } \\\underline{\text { (Income) }}\\\$ 100 \\200 \\300 \\400 \end{array}\begin{array}{c}\\\underline{\text { Tax }} \\ \$ 5 \\15 \\30 \\50\end{array}\begin{array}{c}\text { Base } \\\underline{\text { (Income) }}\\\$ 100 \\200 \\300 \\400 \end{array}\begin{array}{c}\\\underline{\text { Tax }} \\\$ 30 \\60 \\90 \\120\end{array}\begin{array}{c}\text { Base } \\\underline{\text { (Income) }}\\\$ 100 \\200 \\300 \\400 \end{array}\begin{array}{c}\\\underline{\text { Tax} } \\\$ 10 \\30 \\60 \\100 \end{array}\begin{array}{c}\text { Base } \\\underline{\text { (Income) }}\\\$ 100 \\200 \\300 \\400 \end{array}\end{array}$
Which of the schedules represent(s) a proportional tax?

A) II and IV.
B) III and V.
C) IV only.
D) I only.