The mother didn’t know _____to blame for the broken glass as it happened while she was out.
There are so many viruses on the Internet. If ______ accidentally, the viruses may make your computer break down.
I _______ to your party, but I was prevented by the heavy rain.
---Where did you come across your old classmate Jane? ---It was in the supermarket _______ she worked _______ I came across her.
However, at times this balance in nature is ______, resulting in a number of unforeseen effects.
Harry Potter is said _______ into over twelve languages by the end of last year.