How are scientists planning to apply their studies of these deserts to the future?

We are talking about NASA's scientific projects aimed to forecast the possibilities of human life in other planets such as D-RATS, known as Desert Research and Technology studies. Scientists are planning to apply their studies of these deserts to the future of humankind. OT The Ames Research Center in the Mojave Desert, California, operated by NASA, focuses its efforts on developing research such as the Space-ward Bound to share this valuable information with teachers who can share their experience with their students at school.  

Explanation:

it is a better alternative

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."