What were some of the things that Europeans needed in order to begin to sail on the ocean and find an all water route to Asia?

compass and the astrolabe

Explanation:

The compass and the astrolabe were needed by Europeans to begin to sail on the ocean and find an all-water route to Asia. Also, these tools helped explorers to sail across the Atlantic Ocean. The compass has a magnetic needle that always points towards the north. This needle can spin freely. So,  a ship’s navigator could find the other  directions if he knew which direction was north.

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."