Dr.Vallenas says many mothers are discouraged from breast-feeding because they do not know how to get their baby to latch on properly to the breast's nipple, or because they suffer pain and discomfort.

VOA: standard.2009.08.01

But Chad Reissig says scientists do not know a lot about them and how they interact with each other and caffeine.

VOA: special.2009.07.22

They do not know why da Vinci painted it, or how it ended up in the collection of French ruler Francis the First.

VOA: special.2010.06.23

We are worried because we do not know how long they will stay or how we will take care of them.

VOA: standard.2009.10.27

How do we know that they are not going to keep it all?" The United States and allies France and Russia have supported the IAEA draft deal with Iran as a means to alleviate concerns that Tehran is using its nuclear program to develop atomic weapons covertly.

VOA: standard.2009.10.28