premise: Christiana Securities Company and Delaware Realty + Investment Company , major stockholders in du Pont , and the stockholders of Delaware were dealt with specially by provisions requiring the annual <mask> by a trustee , again over a ten year period , of du Pont 's General Motors stock allocable to them , as well as any General Motors stock which Christiana and Delaware owned outright .
hypothesis: the proper context for <mask> here should be a particular instance of selling