If that requirement seems demanding, Shakespeare's sonnets are also written in iambic pentameter.

VOA: special.2010.01.06

One requirement is that the permanent collection cannot be changed.

VOA: special.2009.01.11

"But then,at the top of the pyramid, you have a small-but-growing group of entrepreneurs in China who see that greening their business is not just a legal requirement, nor a responsible act to do.

VOA: standard.2010.02.24