Rachel is describing an event in a narrative piece she is writing which sentence use a transitional word that best indicates a shift from one time frame to another ?

a. when we made it back to shore , we were exhausted but happy to be back on land .
b. it took us an hour to paddle over to the other side of the lake and back.
c. kayaking on the lake is fun , but we didn’t realize how far we had gone.
d. since then , we had decided to kayak along the shoreline on this side of the lake.