Grand Canyon is the proper noun
The answer may be A, if not it will be D. I hope this helped! (: If you ever need help in English, Biology, Veterinary Science, (which are my best subjects), you can always come to me. (:
Answer:
"which became popular in the 1960s"
Explanation:
"which became popular in the 1960s" is the answer because is starts with 'which'