In a circuit diagram (figure $1$) containing three light bulbs labeled $A$, $B$, and $C$, which of the following pairs of bulbs are connected in series to each other?

• A. Bulbs $A$ and $B$
• B. Bulbs $B$ and $C$
• C. None of the bulbs are connected in series
• D. Bulbs $A$ and $C$

Answer: (A)

Verified step by step guidance

1. Recall the definition of bulbs connected in series: two bulbs are in series if they are connected end-to-end so that the same current flows through both without branching paths between them.
2. Examine the circuit diagram carefully to identify the path of the current and see how the bulbs are connected relative to each other.
3. Check if there is a single path that passes through both bulbs without any junctions or branches in between; if such a path exists, those bulbs are in series.
4. Compare each pair of bulbs (A and B, B and C, A and C) to see if they meet the series connection criteria based on the wiring shown in the diagram.
5. Conclude which pair(s) of bulbs are connected in series by confirming that the current flows sequentially through them without splitting or merging paths.