This is a very interesting bookI’ll buy it，

It suddenly occurred to him ____ he had left his keys in the office．

The old lady died from the _____on herhead; she was _______when cleaning windows on the ladder when she fell off it.

The Pacific region will be one of the fastest growing areas in the world in the 21st century ______ shouldn’t be any doubt about it now

It is along time _______they separated, but it won’t be long ____ they meet again.