CREATE TABLE "challenger_limited_selected_clients" (
  "client" text,
  "years_of_operation" text,
  "area_of_operation" text,
  "country" text,
  "services" text
);

Question: Whose address of operation was the Echirax Concession? 
SQL: SELECT "client" FROM "challenger_limited_selected_clients" WHERE "area_of_operation"='EchiraX Concession';

Question: When was the operation in Field 103 executed? 
SQL: SELECT "years_of_operation" FROM "challenger_limited_selected_clients" WHERE "area_of_operation"='Field 103';

Question: In what country is the El Hamada area of operation? 
SQL: SELECT "country" FROM "challenger_limited_selected_clients" WHERE "area_of_operation"='El Hamada';