If measure of an unequal angle of an isosceles triangle is \[90{}^\circ ,\] which one of the following is the measures of one of the equal angles?

• A.  \[45{}^\circ \]
• B.  \[50{}^\circ \]
• C.  \[55{}^\circ \]
• D.  \[60{}^\circ \]
• E.  None of these