A new report challenges the view that governments must check global warming.

The report does not challenge the value of aspirin in preventing a second heart attack in someone who has had one.

Several reports have challenged the validity of the prescribing unit.

These same reports, in the mid-1950s, challenge the lifetime of the university, which was not the case in the previous years.

The report challenges the Government's claims that generating energy from wind power will be cheaper in the long run.

"The report does not challenge the commitment of the commissioner or the department to achieving reform," he said.

The report also challenges Americans to take the full measure of risk that is inherent in space travel.

The report challenges the city's commitment to affirmative action.

The report challenges the conventional wisdom that care quality suffers when providers look after more than one or two children.

The new report does not challenge these findings.