Please choose the correct ending to complete the given sentence: Food and Entertaining: [header] How to build a tunnel [title] Consider where the tunnel will be built. [step] The proposed tunnel's location will determine what tools and techniques are necessary to construct it and prepare it for its intended use. Tunnels can be divided into 3 types : [substeps] Soft-ground tunnels.

Ending1: These can be built in high-intensity, since they require no tools or blueprints. Hot-ground tunnels are actually excavated and filled with electrical material. Ending2: They are usually either set aside or put down in shady, warm or dimly lit spots. They will provide shade for insects and animals. Ending3: Small tunnels: no smaller than 1 m. Natural tunnels: no larger than 3 m. Ending4: These tunnels require support at the openings to keep the tunnel from collapsing. These tunnels are usually shallow and used for subways, water delivery, and wastewater removal systems.

Answer format: ending1/ending2/ending3/ending4