But contained in the strategy are many unknowns and as Mr.Brown said, he is also dependent on the decisions of others.

VOA: standard.2009.11.10

Mr.Obama will interrupt a family weekend at the Camp David presidential retreat on Monday to lay a wreath at the Tomb of the Unknowns at Arlington National Cemetery.

VOA: standard.2009.05.23

But observers say there are plenty of unknowns, including whether Iran will cooperate with the tentative deal and to what extent the IAEA will be able to monitor Iran's nuclear efforts.

VOA: standard.2009.10.19