GMAT Sentence Correction (SC) | Sales of wines declined in the late 1980s, but they began to

Please help me to identify clauses and subject verb in the question stem.
Please review below:
Sales- Subject
of wines- prepositional phrase
declined- verb
in the late 1980s- prepositional phrase
Sales......1980s- this is IC
IC, but IC- after but we need an independent clause

After but- 'they' refers to sales- they is subject?
began- Is this verb here?
to grow- is not a verb
again...1991 report - prepositional phrase
that- Subject?
linked- verb?

Please confirm