Which Link Would We Train First, If We're Doing Backward $\rightarrow$

Multiple Choice

Which link would we train first, if we're doing backward chaining?

A) Rat pulls chain $\rightarrow$ Light on
B) Light on $\rightarrow$ Rat presses lever $\rightarrow$ Dipper click
C) Dipper click $\rightarrow$ Rat approaches dipper $\rightarrow$ Rat receives water