The circuit is working, and all three bulbs are lit. if a switch at c is opened, what will happen to the circuit? a. all three bulbs will stay lit. b. bulbs 2 and 3 will go out, but bulb 1 will remain lit. c. bulb 3 will go out, but bulbs 1 and 2 will remain lit. d. all three bulbs will go out.

The correct answer is option D.All three bulbs will go out.

In the circuit, all the bulbs are connected in series with each other. When the switch at C is opened, the circuit is broken (consider the wire is broken). It is shown in diagram as well (attached).

Hence, when the circuit is broken, the current will not reach the bulbs 2 & 3. And, the connection will be disrupted, So all the bulbs will blow out.

Hence, D is the correct option.