With the A. migration of people from fertile areas, knowledge of agriculture spread by diffusion.
When people migrate from a place, they move into other areas. When something diffuses, it spreads around.
Polygamy began to end when agricultural development and settling got introduced. During the nomadic non-agricultural period, polygamy was common and people were not tied to a single person.
Tired from practice, AND Spending too much time preparing for a match
Participial phrases are verb phrases that act as adjectives to describe nouns. Putting these participial phrases into a sentence makes it easier to see how this works. Tired from practice, Justin decided to take a nap before doing his homework. In this sentence, "tired from practice" describes Justin. Spending too much time preparing for a match, Justin felt unprepared for his Calculus test. "Spending too much time preparing for a match" also describes Justin.