As our van pulled up to the ranch (牧场) to start a three-month program for troubled boys, we passed a cowboy on his horse. Bill was the owner of the ranch. We made eye contact through the dusty window and he winked (挤眼睛) at me and touched the brim of his cowboy hat in welcome.All summer long Bill and his ranch-hands taught us to ride horses, chop wood, and round up cattle. We started to understand the value of working with our hands. Knowing how important it was for boys like me to know that someone believed in them, he trusted us to do the job and do it right. We never let him down.The last day at the ranch, Bill pulled me aside and praised me for the work I had done-- not only on the ranch, but also on myself. He told me if I ever needed anything I could count on him.Four years later, I took him up on that offer. I called him up and asked for a job. I told him how his confidence in me had given me the’ courage to change my life. He offered me a job on the spot. I’m proud to say that each summer I’m the one in the ranch to open the gate for a van full of young men who need someone to believe in them, so they can learn to believe in themselves. By "Four years later, I took him up on that offer" (Para 4), the author means that （）

A. he admired Bill for that offer
B. he offered Bill help in return
C. he accepted Bill’s offer
D. he remembered Bill’s offer