"To accommodate for lack of dependable rainfall" would be the best option as to why the ancient Chinese organized large groups of people to build and maintain irrigation systems, since when rainfall would not come for long periods of time, the crops would likely die without proper irrigation.
This is a personal question, which means that only you can answer it. However, I can give some examples that might help guide your work.
An example of a primary source that you might encounter in your own life is that of a news article. As this article is likely to be written by a reporter witnessing the events, it can be considered a primary source. On the other hand, an example of a secondary source would be a non-fiction book that talks about a historical event. This is because such a book would give a second-hand account of an event based on historical information.
Answer: B. Helping civilizations grow lots of food
Explanation: APEX
She is <span>B. Mama Quilla
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He launched Operation Linebacker. He bombed Hanoi and Haiphong that led to the
destruction of the North’s economic and industrial centers. He continued the bombings and also threatened to withdraw U.S. and end the agreement. Nixon halted the bombings and signed the
Paris Peace Accord that ended U.S. involvement in the area.
