Please choose the correct ending to complete the given sentence: Computers and Electronics: [header] How to build an airsoft artillery piece [title] Make a base block. [step] Use a good, strong piece of wood about 2 feet (0.6 m) by 2 feet (0.6 m). This will be what everything else is built on.

Ending1: Your base block should be about 4 feet (1.2 m) wide and 4 feet high. This is the ideal block for an airsoft artillery piece. Ending2: ( for the mortar and mortar, make sure any building blocks that you use are adequate. ) [substeps] Use polyurethane or fiberglass for medium-strength builds. Ending3: [title] Get a 2 by 4 approximately 4-5 feet (1.2-1.5 m) long. [step] Attach this to the top center of the 2 by 2 foot board with the end of the 2 by 4 matching up with the opposite side of the board so now it sticks out. Ending4: A base block is not a piece of wood, it is a solid piece of material like a wall or door. So make sure it is as strong as possible.

Answer format: ending1/ending2/ending3/ending4