1. Three of four, and all four are reading

Note. THREE OF FOUR, SO YOU DROP EXACTLY ONE, AND ALL FOUR ARE FREE. Nothing here needs to be bought, visited or arranged, so choose by what you would rather be able to talk about. 1(b), one real railroad researched in four dimensions, is the most work and by some distance the most useful, because it turns every other requirement on the badge from an abstraction into a description of a company you now know something about. 1(c) is the quickest if you have pictures to hand, and its purposes are the requirement rather than the names. 1(a) turns on one idea, that a unit train never has to be taken apart and reassembled along the way. 1(d) is the most technical, and its two named terms, dynamic braking and radial steering trucks, are vocabulary to look up rather than reason out.