What led many ex-slaves to migrate west and north? the invention of the cotton gin
the cotton boom
the election of Abraham as president
the emancipation of the slaves

Whether or not a given study has the possibility of causing harm to participants:

As you drive in to school, you hear a random radio-show caller arguing that sun exposure really has not been shown to cause skin cancer and that some research suggests that skin cancer is completely genetic and not related to sun exposure at all. at the time, you think that this is a silly argument and that the caller does not know what she is talking about. however, two months later, you are outside without wearing sunscreen, and you find yourself remembering that you had read something about how the sun actually does not cause skin cancer. this process is evidence that has influenced your attitude

The development of simple stone tools by early hominids led to the ability to procure meat more efficiently. this in turn led to the change in diet that included larger amounts of protein. many scholars believe that this shift in diet was a significant part of how our ancient ancestors adapted so quickly to a varied set of environments, and thus were able to begin cultural development. this demonstrates the intimate connection between