解答上述试题---**Extraction Content:** **Question Stem:** [例 2] 在图 4 - 4 - 1 所示的家庭电路中， 火线 安装中发生错误的电路元件是 ( ) **Options:** A. 开关 S₁ B. 灯泡 L₂ C. 插座和开关 S₂ D. 带有保险丝的闸刀开关 a **Chart/Diagram Description:** * **Type:** Electrical Circuit Diagram (Household Circuit Diagram). * **Title/Label:** 图 4 - 4 - 1 * **Main Elements:** * **Input Lines:** Two main input lines are shown: one labeled "火线" (Live wire) at the top, and one labeled "零线" (Neutral wire) below it. * **Main Switches/Fuses:** * The Live wire passes through an open switch, then connects to the top input of a double-pole knife switch. * The Neutral wire passes through another open switch, then connects to the bottom input of the double-pole knife switch. * One pole of the knife switch (connected to the live line) contains a fuse, and this entire component is labeled 'a'. * **Load Branch 1 (Socket):** * After the knife switch 'a', the live line connects to one terminal (left-hand pin) of a three-hole socket. * The neutral line connects to the other two terminals (right-hand pin and top pin) of the three-hole socket. * **Load Branch 2 (Lamp L1):** * After the knife switch 'a', the live line also connects to one side of a switch labeled S₁. * The other side of switch S₁ connects to one terminal of a lamp labeled L₁. * The other terminal of lamp L₁ connects to the neutral line. * **Load Branch 3 (Lamp L2):** * After the knife switch 'a', the live line also connects to one side of a switch labeled S₂. * The other side of switch S₂ connects to one terminal of a lamp labeled L₂. * The other terminal of lamp L₂ connects to the neutral line. * **Connections:** The three load branches (socket, L1, L2) are connected in parallel across the live and neutral lines after the main fuse and switches. * **Labels and Annotations:** * "火线" (Live wire) * "零线" (Neutral wire) * 'a' (label for the knife switch with fuse) * S₁ (label for a switch) * L₁ (label for a lamp) * S₂ (label for a switch) * L₂ (label for a lamp) * Socket symbol (three-hole, appearing as a circle with three dots) * Lamp symbols (circle with a cross inside) * Switch symbols (open switches) * Fuse symbol (rectangular box within the knife switch 'a' symbol) * **Relative Position and Direction:** * The live and neutral wires are shown entering from the top-left. * The main protection (switches, fuse 'a') is near the entry point. * The loads (socket, L1 with S1, L2 with S2) are arranged in parallel to the right. * Switches S1 and S2 are placed on the live side of their respective lamps L1 and L2. * The three-hole socket has its left terminal connected to the live wire, and its right and top terminals connected to the neutral wire.