What precautionary measures must be taken before putting a loading crane into operation?

You answered correctly. Before operating a loading crane, it is essential to secure the vehicle against tilting using the side supports to ensure stability and safety during lifting. Additionally, there must not be any electrical lines within the crane's swivelling range to prevent the risk of electrocution or electrical accidents. Both measures are required safety precautions according to German traffic rules for operating loading cranes. The third option, checking if support is necessary, is not a mandatory safety measure; the focus is on securing the vehicle whenever the crane is used.