Which resistors in the circuit must have the same amount of charge passing through each second?

Resistors 'C' and 'D' are in series.  There's only one possible route for current to flow through them.  Every electron that flows through one of them has to flow through the other one.  So the current (amount of charge per second) must be the same in 'C' and 'D'. (answer-choice B)

connect the batteries in series and hope