Why must scientists cut a thin slice from a biological specimen before they can do it under a microscope?

if you are on the computer you can not take a picture but you can upload one but i am not sure about phones but i'm pretty sure it's the but to upload one just click the paper clip looking thing/ link thingy thing and upload a pic

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."