Please choose the correct ending to complete the given sentence: Education and Communications: [header] How to add lead to a mechanical pencil [title] Replace cassettes. [step] Exact instructions may vary by model, but generally, start by pulling the eraser out of the pencil, which will draw out the old cassette. Give the old cassette a shake just to make sure that it really is empty.

Ending1: Then, for the new cassette, place a few drops of lead in the empty cassette slot. Set the fill-in slot to the left of the original cassette slot and press the " go " button to fill it in. Ending2: If so, insert a new cassette into the pencil's open chamber. Once it clicks into place, reinsert the eraser after detaching the old cassette. Ending3: Replace the new cassette in the same manner that you removed it from inside the pencil. [substeps] Antifreeze is preferred over nitrate, so cut across any grooves or curves when done. Ending4: Then, replace cassettes again with the new cassette. [title] Consider substituting substitutes to improve your ratio of lead to other material.

Answer format: ending1/ending2/ending3/ending4