which museum exhibits the portrait of the count-duke of olivares by diego velázquez ?
select distinct var_uri where brack_open dbr_Portrait_of_the_Count-Duke_of_Olivares_ attr_open Hermitage attr_close dbo_museum var_uri sep_dot dbr_Portrait_of_the_Count-Duke_of_Olivares_ attr_open Hermitage attr_close dbo_author dbr_Diego_Velázquezbrack_close