At the core of biology and other sciences lies a problem-solving approach called the scientific method. 1  Make an observation. 2  Ask a question. 3  Form a hypothesis, or testable explanation. 4  Make a prediction based on the hypothesis.  Test the prediction.
Xi. Xi is the 14th letter of the Greek alphabet. It is pronounced in Modern Greek, and generally or in English. In the system of Greek numerals, it has a value of 60. Xi was derived from the Phoenician letter samekh. Xi is not to be confused with the letter chi, which gave its form to the Latin letter X.
Xi'an is more than 3,000 years old and was known as Chang'an (é¿å®) in ancient times. For 1,000 years, the city was the capital for 13 dynasties, and a total of 73 emperors ruled here. Xi'an is the undisputed root of Chinese civilization having served as the capital city for the Zhou, Qin, Han, Sui and Tang dynasties.