Which circuit consists of four sections connected in series to form a closed loop?

• A. Amplifier
• B. Autotransformer
• C. Amplification
• D. Bridge circuit

Answer: (D)

Four sections arranged around a loop define a bridge circuit. In a bridge, four impedances are connected in a closed path so current can flow through each section in sequence around the loop, typically with a detector placed across a diagonal to compare opposite points (as in a Wheatstone bridge). This four-arm loop is the defining feature of a bridge circuit, setting it apart from the other options. An amplifier is just a device that increases signal strength, an autotransformer uses a single winding with a tap, and amplification refers to the process itself, not a four-section loop topology.