The core element of a fan needs identification. Analyzing potential components: (1) Current: Electric fans utilize current, unlike manual or water-powered fans. (2) Switch: Electric fans often include switches, but this is an external control. Hand fans lack switches. (3) Regulator: Speed regulators are not universal, absent in some designs (e.g., single-speed fans, hand fans). (4) Blades: Air movement via rotating blades (or vanes) defines a fan's function. Blades are critical, regardless of power source. Consequently, blades are the consistent component. This aligns with option (4).