Which one is false under the following statements about repurchase agreements

A、repurchaseagreementisakindofmortgagebackedbysecurity;
B、thesecuritiestradedinrepurchaseagreementsareprimarilycorporatebonds;
C、reverserepurchaseagreementsandrepurchaseagreementsaretwoaspectsofthesameproblem;
D、deliveryofsecuritiesinrepurchaseagreementsgenerallydoesnottaketheformofphysicaldelivery,especiallyinshortertermrepurchaseagreements