\def\baseclass{book}
\DeclareOption*{\PassOptionsToClass{\CurrentOption}{\baseclass}}
\def\@checkoptions#1#2{
\edef\@curroptions{\@ptionlist{\@currname.\@currext}}
\@tempswafalse
\@tfor\@this:=#2\do{
\@expandtwoargs\in@{,\@this,}{,\@curroptions,}
\ifin@ \@tempswatrue \@break@tfor \fi}
\let\@this\@empty
\if@tempswa \else \PassOptionsToClass{#1}{\baseclass}\fi
}
\@checkoptions{11pt}{{10pt}{11pt}{12pt}}
\PassOptionsToClass{a4paper}{\baseclass}
\ProcessOptions\relax
\LoadClass{\baseclass}