If you had to choose the single most important ___________(discover) of the 20th century, you would have a real _________ on your hands. In just 100 years, the world changed completely. Amazing discoveries were made in medicine, communications and transport, not to ____________ our knowledge of the world and space. Medical advances ________  from discovering the causes of diseases under microscopes to surgical procedures ____________(replace) __________(disease) organs with ________ (donate) ones. Communications changed ______ the introduction of mobile phones and the way we __________(通信) went ________ writing letters to emailing. We started flying around the world and ____________（同时）, scientists figured ________ how to ______(劈开) the atom,________（过去） thought to be the smallest particle of matter ______  the universe.