name the river whose source place is nakashibetsu and mouth place is shibetsu ?
SELECT DISTINCT var_uri where brack_open var_uri dbo_sourcePlace dbr_Nakashibetsu,_Hokkaidō sep_dot var_uri dbo_mouthPlace dbr_Shibetsu,_Hokkaidō sep_dot var_uri a dbo_River brack_close