Problem Nineteen. A stationary electron$-$positron pair emerge from the vacuum as virtual particles.

$($THIS IS AN EXAM QUESTION.$)$

$28.$ Find the maximum time that the pair can exist in units of $10-22$ s$.$

$($A$)1\mathrm{.}65($B$)3\mathrm{.}06($C$)1\mathrm{.}86($D$)2\mathrm{.}38($E$)3\mathrm{.}22$