who is the common prime minster of john spencer-churchillr and robert gascoyne-cecil ?
SELECT DISTINCT var_uri where brack_open dbr_John_Spencer-Churchill,_7th_Duke_of_Marlborough dbo_primeMinister var_uri sep_dot dbr_Robert_Gascoyne-Cecil,_3rd_Marquess_of_Salisbury dbp_primeminister var_uri brack_close