It is reported that there is a $1000 _________ for any information that helps police find the lost relic.

She expressed ________to the teachers for helping her pass the College Entrance Examination.

The lack of eco-friendly habits among the public is thought to be a major _____of global climate change.

Chest pains can be a  warning ____of heart problems.

After three months, these young students finally became used to the ______ of life in a big city abroad.