中產階級

中 = 丨 + 口 : Mnemonic symbol: a dart board, because you always try to hit the center.

Julian Giant Squid (zhu-) is throwing dinosaur bones (丨) as darts on a dart board in front of the engine ((e)ng1). To make it a bit more difficult he's throwing mandarins (口) into the air as well and skewers them up right in the center (中 is a mandarin skewered on a dinosaur bone) in mid flight with the dinosaur bones. He's still able to consistently hit the center (中) of the dart board.

产 = 厂 + 立 : Mnemonic symbol: an assembly belt. Can you see the vase soon falling off the assembly belt?

In anthill, Charlie Chaplin is setting up his assembly line. At the one end there is a supply of vases. In the middle of the assembly line, a chocolate factory fills chocolate into the vases. At the other end, the little vases with the chocolate are dumped into a large vase.

阶 = 介 + 阝 : The pope (阝) sentenced Joan of Arc (ji) to death and wants to shoot her to outer space using a rocket (介) in front of the elevator (e1). He doesn't have a proper launch ramp, so he just uses some stone stairs (阶).

级 = 及 + 纟 : Joan of Arc (ji) closely investigates her newly arrived troops just inside the space station's entrance (Ø2). She ranks (级) them according to their level (级): First there is a silk worm (纟) which can at least shapeshift. On the next level, there is Yuwen Huaji (及), who has no comparable super power.