XR, used as an umbrella term in this field, stands for

The correct answer is B, additive manufacturing. The name comes from the method: material is added layer upon layer under the control of a digital model until the object is complete, so that nothing has to be cut away. Option A is wrong because subtractive manufacturing is the exact opposite, in which a solid block is cut, drilled, turned or milled until the required shape is left, as on a lathe. Option C is wrong because formative manufacturing refers to shaping a material by applying force without adding or removing it, such as forging, casting or injection moulding. Option D is wrong because reductive manufacturing is not a recognised term in the field; it is offered only because it sounds like the opposite of additive and so tempts a candidate who has learnt the contrast but not the names.

The correct answer is A, Chuck Hull. He invented stereolithography in the mid-1980s, in which a laser hardens liquid photopolymer resin point by point, and in doing so built the first working 3D printer; he also went on to found a company to sell the machines. Option B is wrong because Jaron Lanier is associated with virtual reality, a phrase he popularised, and not with printing. Option C is wrong because Ivan Sutherland built the first head-mounted display in 1968, the device nicknamed the Sword of Damocles, which again belongs to the reality technologies. Option D is wrong because Neal Stephenson is a novelist who coined the word metaverse in Snow Crash in 1992. All four names belong to this topic, which is why they are set together.

The correct answer is B, STL. An STL file describes the outer surface of a three-dimensional object as a mesh of triangles and carries no colour, material or texture information. A design made in computer-aided design software is exported as STL, and a slicing program then cuts it into horizontal layers and writes the machine instructions, usually G-code. Option A is wrong because JPEG is a compressed format for flat photographic images and has no depth information at all. Option C is wrong because MPEG is a family of standards for compressing video and audio. Option D is wrong because PDF is a format for fixed-layout documents meant for reading and printing on paper, not for driving a printer that builds in three dimensions. Candidates should remember that the STL file stores geometry alone, which is why colour printing needs newer formats built on top of it.

The correct answer is C, computer numerical control milling. Milling on a computer-controlled machine is a subtractive process: a rotating cutter removes material from a solid block until the shape remains, so no layers are added. Option A is wrong because fused deposition modelling is an additive process in which a heated nozzle extrudes a thermoplastic filament layer by layer. Option B is wrong because selective laser sintering is additive too, fusing grains of polymer powder together with a laser where the object is to be solid. Option D is wrong because stereolithography, the oldest of the three, is additive: a laser cures liquid resin point by point. Slipping a machining process in among printing processes is the standard way this question is set. It is worth noting that additive and subtractive methods are often combined in practice, a printed part being finished on a milling machine to get an accurate surface.

The correct answer is B, Snow Crash by Neal Stephenson. The novel, published in 1992, uses the word metaverse for a shared virtual city that people enter through goggles and move about in as avatars, and the term was taken up decades later for persistent three-dimensional online worlds. Option A is wrong because Neuromancer, published in 1984, gave the world the related term cyberspace, not metaverse. Option C is wrong because Ready Player One, a later novel, describes such a world but did not name it; it borrows from the idea rather than coining it. Option D is wrong because the Sword of Damocles is not a book at all but the nickname of the head-mounted display Ivan Sutherland built in 1968, the first of its kind.