It’s already 10:00, I wonder how it _______ that she was two hours late on such a short trip.
______ surprised the family most was ________ the girl played basketball very well.
Someone is ringing the doorbell. Let’s see _______.
It is very common that former people have difficulty in _____ modern life.
I really don’t know ___ ___I kept the secret papers.
---Why do you look so upset? ---There are so many troublesome problems ____.