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 the oldest of the Four Great Ancient Capitals of China, having held the position under several of the most important dynasties in Chinese history, including Zhou, Qin, Han, Sui, and Tang.he original Xi'an city wall was started in 194 BCE and took 4 years to finish. Upon completion, the wall measured 25.7 km (15.97 mi) in length and 12 to 16 m (39.37â52.49 ft) in thickness at the base, enclosing an area of 36 km 2 (13.90 sq mi).