Medical experts say small amounts of carbon monoxide over a long period of time can greatly harm an unborn baby.

VOA: special.2010.02.02

The unusually long period of cold weather has shown how even warm climates can sometimes freeze over.

VOA: special.2010.01.12

Doctors use it to control moderate to severe pain over a long period.

VOA: special.2009.02.10

The results suggested that people do act differently if they think they are working with a group for a short period of time instead of a long period.

VOA: special.2009.03.03

So,to get a sense of what the regional moisture patterns have been, dryness and wetness over such a long period of time in great detail, I would call it a kind of victory for paleoclimate science."

VOA: special.2010.05.25

"This experiment is unique because six people will be isolated for a long period of time and will work autonomously."

VOA: standard.2010.06.02

No single space project in this period will be more impressive to mankind or more important for the long range exploration of space.

VOA: special.2009.07.08

Long-period comets,however, may take several hundred years to orbit the sun.

VOA: special.2011.02.09

Each exercise period should be at least ten minutes long.

VOA: special.2010.06.08

"Now the Long March is for an indefinite period.

VOA: standard.2009.03.15