Suppose that the Treasury bond futures price is 101-12. Which of the following four bonds is cheapest to deliver?
$$
\begin{array}{lcc}
\hline \text { Bond } & \text { Price } & \text { Conversion factor } \\
\hline 1 & 125-05 & 1.2131 \\
2 & 142-15 & 1.3792 \\
3 & 115-31 & 1.1149 \\
4 & 144-02 & 1.4026 \\
\hline
\end{array}
$$