Identify the sentence which contains a subordinating connection.
a. after a brief stop at the rest area, we continued our drive on the interstate.
b. although the stop was short, we were for time to stretch our legs during a quick walk around the park.
c. the rest stop had an area for picnic tables, and we decided that next time we would bring a picnic lunch for our return trip.
d. as a result, we bought a cooler and made sandwiches for our trip back home.