What are the two types of circuits?

• A. AC and DC circuits
• B. Parallel and series circuits
• C. Circuit elements and protective devices
• D. Open and closed circuits

Answer: (D)

The key idea is whether the path for current is continuous. A closed circuit has a complete loop from the power source, through conductors and the load, back to the source, so current can flow and the device operates. An open circuit has a break in that path—like a switch left open or a damaged wire—so no current can flow and the device stays off. This simple distinction explains why a switch being on or off changes whether power reaches the load, and it’s the basic test idea behind identifying open versus closed circuits. The other concepts describe different aspects of circuits (how current moves, how components are arranged, or what devices exist), but they don’t address the presence or absence of a complete conducting loop.