Read these sentences from a concluding paragraph. By around 1700 BCE, most of the cities along the Indus River had been abandoned.
The Indian monsoon rains had weakened, causing less extensive floods, and as a result, less food was grown.
The reduced water supply caused the Indus River valley’s population to move eastward toward the Ganges River valley.
Which statement best describes the purpose of sentence 1?

It develops the topic.
It restates the essay’s thesis statement.
It reviews evidence presented to readers.
It summarizes the main ideas of the essay.