Which of the following sentences is correctly punctuated?
a. Mary remembered to buy milk didn't she?
b. The local police asked the F.B.I. to assist with the case.
c. Mr. Jones visited the YMCA before becoming a member.
d. The company held it's annual party at the convention center.

How is a compound sentence formed?
a. By joining a simple sentence with a dependent clause
b. By joining two independent clauses and one dependent clause
c. By joining two simple ...

I will correct the sentences: (changes between exclamation marks)

a. Mary remembered to buy milk !,! didn't she? (comma needed)
b. The local police asked the !FBI! to assist with the case. (periods are false)
c. Mr. Jones visited the YMCA before becoming a member.
correct sentence!
d. The company held !its! annual party at the convention center. (its is misspelled)

A compound sentence is formed by joining two independent clauses - so I think that option c is best, although I am unsure what the three dots stand for?