Why do duplicates in experiments?

What organization helped Haiti earthquake? How is humidity measured electronically? What effect will the wind have on the way a rocket is launched? If you remove the letters t a and i from the name of a certain element you'll have the name of a nocturnal pouched animal. what is the element? What is the most active volcano of the 19th century? What sound does a penguin make? How do similar and opposite sides of a magnet interact with other magnets? How can scientists help to prevent a natural process from becoming an enviromental hazard? How do the guard cells behave during the day? What are the consequences of the earths rotation? Is energy abiotic or biotic? Are Chloroplasts enclosed within a single membrane.? How is carbon dioxide fixed in the atmosphere? What are the characteristics of the stomach? How far is the international date line from Alaska? What does But old folks many feign as they were dead - Unwieldy slow heavy and pale as lead mean? What two types of observations that can be used to indicate flow rate? Which animals are facultative carnivores? What is the time difference between Holland and the UK in May? What is the winter weather like in Midland Texas?