Because he didn't study hard enough for his exam, Ryan couldn't pass it.→
Not having studied hard enough for his exam, Ryan couldn't pass it.
As I had been to England before, I knew where to find a good hotel.→
Having been to England before, I knew where to find a good hotel.
Waiting for the doctor,（a the alarm went off b Dave read a magazine c a big noise scared everybody）. (a, b, cより選ぶ）
Waiting for the doctor, Dave read a magazine.