bbc英語聽力練習(xí)：Citizen scientists

evidence
    facts that make you believe something is true
    extraterrestrial intelligence
    advanced life forms existing beyond our planet
    clues
    pieces of evidence
    analyse
    examine
    volunteers
    people who do something without being paid for it
    vital
    essential
    age-old
    long-standing or very old
    astronomers
    people who study space
    citizen
    person belonging to a particular country
    tantalizing
    exciting, making you want more (even if it is not possible)
    exists
    occurs