What is the reason for British invasion in Africa

Africa's natural resources

Explanation:

 Africa's valuable resources such as gold, ivory, salt and more, they did not hesitate on conquering the land. They wanted these resources because they needed them for manufacturing. Another resource in Africa was rubber which was very helpful and used in making many good-selling items like shoes.

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."