The correct answer is D) 'R1', 'R2', and 'R3' are connected in series. This is correct because in a series circuit, the components are connected end-to-end, forming a single path for the current to flow through. The current is the same through each component, and the total resistance is the sum of the individual resistances (R1 + R2 + R3). The other options are incorrect because: A) In a parallel circuit, the resistors are connected to the same two points, and the total resistance is the reciprocal of the sum of the reciprocals of the individual resistances. B) This formula applies to parallel circuits, not series circuits. C) In a series circuit, the voltages across individual resistors are not necessarily equal.