In the "Bathtub Model" of Unemployment, the Key Equation Is $\bar { L } = U _ { t } - E _ { t }$

In the "bathtub model" of unemployment, the key equation is:

A) $\bar { L } = U _ { t } - E _ { t }$
B) $\bar { s } E _ { t } = \bar { f } U _ { t }$
C) $\bar { s } E _ {t } = \bar { f } \bar { L }$
D) $\bar { f } E _ { t } = \bar { s } U _ { t }$
E) $\bar { s } E _ { t } = ( 1 - \bar { f } ) U _ { t }$