Analyze the sentence to determine the main clause and the subordinate clause. then choose the function of the subordinate clause.

the mason-dixon line, which is perhaps the most famous border ever established by surveying methods, has been designated a national historic civil engineering landmark.

1.main clause:
a. the mason-dixon line
b. the mason-dixon line, which is perhaps the most famous border ever established by surveying methods
c. the mason-dixon line has been designated a national historic civil engineering landmark
d. the most famous border ever established by surveying methods has been designated a national historic civil engineering landmark
e. has been designated a national historic civil engineering landmark

2.subordinate clause:
a. which is perhaps the most famous border ever established by surveying methods has been designated a national historic civil engineering landmark
b. has been designated a national historic civil engineering landmark
c. which is perhaps the most famous border ever established by surveying methods

3.subordinate clause functions as a(n):
a. adjective
b. adverb
c. noun