Answer:
D. Since then, we had decided to kayak along the shoreline on this side of the lake.
Step-by-step explanation:
This is the sentence that best uses a transitional word to indicate a shift in time. This sentence employs the words "since then." This indicates that the events that will be described occurred in a future time period, and not at the same time as the previous events. Moreover, these words help the author transition from one thought to the next.