This book is not useful for today’s students.
This book is    ▲   for today’s students.
Mary has been in Hong Kong for a month.
Mary    ▲   Hong Kong a month ago.
In the past people thought the earth was flat.
People    ▲   to think the earth was flat.
The family didn’t have enough money to send her abroad.
The family couldn’t    ▲   to send her abroad.
There were about fifteen people in the room, and most of them were women.
There were about fifteen people in the room,    ▲   women.