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

Poets called it the Golden Age. A golden age now describes a historical period of great artistic,scientific or economic progress.

VOA: special.2010.06.06

His early works were influenced by composers of the classical period of the late seventeen hundreds and early eighteen hundreds.

VOA: special.2010.07.12

"I think Dubai went a little bit too fast and they borrowed too much money in a very short period of time."

VOA: special.2009.12.04

He said the most difficult period of the trip was crossing the Yukon Arctic and the Arctic National Wildlife Refuge in Alaska.

VOA: special.2011.03.23

They used information gathered over a period of 20 years, until 2003, in the Framingham Heart Study.

VOA: special.2009.01.21

They found that over a period of six years, planting three rows of trees reduced total dust and ammonia by more than half.

VOA: special.2009.09.08

The rock formations there are the result of deposits made by ancient lakes and rivers over a period of about twenty million years.

VOA: special.2009.04.15

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

VOA: special.2010.01.12

Now there are so many,experts say up to twenty metric tons a day could be removed with nets ver a period of several years.

VOA: special.2009.12.15

Others who want to graduate in three years must pay for the same education as four-year students, but in a shorter period of time.

VOA: special.2009.07.23

The area where the flutes were found has been linked to the Aurignacian culture within the period of history known as the Upper Paleolithic.

VOA: special.2009.08.18

He called for "normalcy" -- a new period of peace and quiet, with few changes.

VOA: special.2010.12.16

During the period of the Cold War, an estimated 30 million people in Eastern Europe and the Soviet Union listened to him on the radio.

VOA: special.2009.01.30