Let H be the subspace of P subscript 3 defined by H space equals space open curly brackets p (x )space equals space a space plus thin space b x space plus thin space c x squared space plus space d x cubed space space vertical line space space a comma space b comma space c comma space d space element of straight complex numbers semicolon space space p apostrophe apostrophe (0 )space equals space 0 close curly brackets where p apostrophe apostrophe (x )space is the second derivative of p (x ). What is the dimension of H