Context: The Catalan verbal system is basically common to all Western Romance, except that most dialects have replaced the synthetic indicative perfect with a periphrastic form of anar ("to go") + infinitive.

Question: What system is common to Western Romance?
Answer: Catalan verbal system

Question: What have many dialects replaced?
Answer: synthetic indicative perfect

Question: What is the Catalan verbal system common to?
Answer: all Western Romance