The Sumerian city-states rose to power during the prehistoric Ubaid and Uruk periods. Sumerian written history reaches back to the 27th century BC and before, but the historical record remains obscure until the Early Dynastic III period, c. the 23rd century BC, when a now deciphered syllabary writing system was developed, which has allowed archaeologists to read contemporary records and inscriptions. Classical Sumer ends with the rise of the Akkadian Empire in the 23rd century BC. Following the Gutian period, there is a brief Sumerian Renaissance in the 21st century BC, cut short in the 20th century BC by Semitic Amorite invasions. The Amorite "dynasty of Isin" persisted until c. 1700 BC, when Mesopotamia was united under Babylonian rule. The Sumerians were eventually absorbed into the Akkadian (Assyro-Babylonian) population.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What was obscure until 2300 BC?
Ah, so.. unanswerable

Valleys and plains are found along the coastline and rivers. The north of the province lies just south of the Yangtze Delta, and consists of plains around the cities of Hangzhou, Jiaxing, and Huzhou, where the Grand Canal of China enters from the northern border to end at Hangzhou. Another relatively flat area is found along the Qu River around the cities of Quzhou and Jinhua. Major rivers include the Qiangtang and Ou Rivers. Most rivers carve out valleys in the highlands, with plenty of rapids and other features associated with such topography. Well-known lakes include the West Lake of Hangzhou and the South Lake of Jiaxing.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What is a well-known lake of Hangzhou?
Ah, so.. West Lake

An early advantage of AC is that the power-wasting resistors used in DC locomotives for speed control were not needed in an AC locomotive: multiple taps on the transformer can supply a range of voltages. Separate low-voltage transformer windings supply lighting and the motors driving auxiliary machinery. More recently, the development of very high power semiconductors has caused the classic "universal" AC/DC motor to be largely replaced with the three-phase induction motor fed by a variable frequency drive, a special inverter that varies both frequency and voltage to control motor speed. These drives can run equally well on DC or AC of any frequency, and many modern electric locomotives are designed to handle different supply voltages and frequencies to simplify cross-border operation.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What taps can provide lighting supply?
Ah, so..
low-voltage transformer windings