Select the correct answer. Read the text below. Use the context to decide the meaning of the word exposure.

Research has demonstrated the usefulness of monitoring when assessing people's exposure to lead in the environment.

in his speech "i have a dream," king states the plight of african americans, as he argues that after the civil war, slaves were promised equal rights and freedoms, but that these promises have not materialized.

he goes on to say that there are those who ask "when will you be satisfied? " implying that african americans alread enjoy a lot. in order to attack this argument, king lists examples of civil rights struggles that african americans still face, such as police brutality, segregation and racial prejudice.