Questions 21-30 refer to the following passage. Revolutions in the quest for new knowledge __21__ many appearances. In biology and medicine, there has been no shortage of breakthroughs that forever change the way we think about a __22__ topic once a new set of observations are collected and shared with colleagues whose ambitions are aimed in a similar direction. The broad spectrum of disciplines comprising our __23__ scientific enterprise continue to seek and obtain “truths” __24__ the benefit of humankind as preventive, diagnostic, and treatment strategies evolve from __25__ they resided 10, 50, or 100 years ago. The __26__ forward in what we perceive as the quest for new knowledge is inextricably linked to advances in technology. In the distant past, the roots of discovery rested firmly in the hands of those able to keenly observe and associate using __27__ the naked eye. Introducing microscopes __28__ the next era of observation and analysis that brought to the surface both cell theory and the cellular basis of disease. Fast forward to the mid twentieth century, when the electron microscope __29__ on the scene. An entirely new landscape of the inner workings of cells, tissues, and the assorted pathogens amongst us revealed a level of organization and complexity that both enhanced and revolutionized our powers of observation and conceptualization when it came to matters of life and death. Enter the world of molecular genetics, and the landscape of biology and medicine has taken up residence in an __30__ universe of new knowledge that students of human health and disease will be wedded to for years to come. (Question 21)