what's the cylinders/ valves with model being 1.8 20v
CREATE TABLE "petrol_engines" (
  "model" text,
  "cylinders_valves" text,
  "displacement_cc" real,
  "max_power_k_w_ps_at_rpm" text,
  "max_torque_nm_at_rpm" text,
  "engine_code" text,
  "top_speed_km_h" real,
  "production_period" text
);
SELECT "cylinders_valves" FROM "petrol_engines" WHERE "model"='1.8 20V';