Question id 168 - Aircraft General Knowledge - PPL(H) - Private Pilot License

Spar of lead and synthetic material, filling material and outer skin of synthetic material, erosion protection of stainless steel
Spar of synthetic material, filling material and outer skin of synthetic material, erosion protection of aluminum
Spar of aluminum and synthetic material, filling material and outer skin and erosion protection of synthetic material
Spar of stainless steel, filling material and outer skin and erosion protection of synthetic material