Final answer:
The Khmer Empire, which is historically significant for Cambodia's beginnings, was established in 802 CE, not aligning with any of the proposed options of 1120 CE, 1200 CE, 1000 CE, or 1100 CE.
Step-by-step explanation:
If we consider the establishment of the Khmer Empire as the beginning of what is now Cambodia, the empire began in the early 9th century. Specifically, the Khmer Empire was established in 802 CE and continued until its decline and the eventual fall in 1431 CE. The empire, at its height, covered much of Southeast Asia, including the territory of modern-day Cambodia. This period was marked by significant achievements in architecture, such as the construction of the Angkor Wat and Bayon Temple. Therefore, none of the options (1120 CE, 1200 CE, 1000 CE, 1100 CE) directly corresponds with the actual beginning of Cambodia's historical identity through the Khmer Empire, which more accurately began in 802 CE.