Allegra, a common prescription drug with the structure shown below, is given for  the treatment of seasonal allergies. How many stereogenic carbon does Allegra possess ?

$C{H_3}CH(OH).COOH$ shows

Total possible stereo isomer from given compound will be

$\begin{array}{*{20}{c}}
  {C{H_3} - CH = CH - CH - CH - C{H_3}} \\ 
  {{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\mkern 1mu} {\mkern 1mu} |{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} \,\,\,\,\,\,\,\,\,\,\,{\mkern 1mu} {\mkern 1mu} |{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} } \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,OH{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} \,\,\,\,{\mkern 1mu} {\mkern 1mu} \,\,\,{\mkern 1mu} {\mkern 1mu} OH\,\,} 
\end{array}\,$

The following compounds differ in respect of 

The absolute configurations of the two centers in the following molecule are

The stereochemistry of this molecule is