Sheng nu cites studies that show that women are now breaking the tradition of "mandatory marriage" to have fewer children or marry later on in life. Other typologically similar terms that are still used in the modern lexicon of other countries and cultures show the concept has existed in some cases as far back as the 16th century. The term spinster was used to describe unmarried or single women of a marriageable age. It wasn't until 2004 when the Civil Partnership Act replaced the word spinster with "single" in the relationship history section of marriage certificates in the UK. Subsequently, at the
White certificates for an obligation. The third phase runs from April 2008 to December 2012 and is intended to deliver 185Mt lifetime savings by 2012. Connecticut, Pennsylvania, and Nevada have adopted Energy Efficiency Portfolio Standards that require regulated utilities to meet a certain percentage of their projected power needs through energy efficiency. Utilities must meet their obligations by either reducing their consumers’ energy usage, or by purchasing energy efficiency certificates (white certificates). More states are expected to follow in the near future. There is also a voluntary market where large corporations are purchasing energy efficiency certificates as a way of meeting their