When walking down the street, I came across David, when I _____ for years.
didn't see
haven't seen
hadn't seen
wouldn't see
I was so familiar with her that I recognized her voice ______ I picked up the phone.
You have to wear a helmet and a life jacket for protection, just ___ you fall into the water. A. in case C. unless C. though D. As
I toured the Great Wall,I was deeply impressed with the beautiful scenery.
He was about to leave the office for home _______someone knocked the door and asked for some help.
If you find yourself ______ no one will help you, please call me.