The correct answer to the question is option 1: crude oil prices. The Brent index is specifically associated with the prices of crude oil. The Brent Crude oil price is widely used as a benchmark for pricing and trading in the global oil market. It represents the average prices of oil produced from several oil fields in the North Sea, specifically in the Brent and Forties oil fields. The index serves as a reference point for determining the value of oil in various transactions, including futures contracts and physical supply agreements. It is an important indicator for the global energy market and often reflects trends and fluctuations in oil prices worldwide.

Option 2: copper future prices is not correct because the Brent index is not associated with copper. Copper futures have their own separate benchmark indices.

Option 3: gold future prices is also not correct. While gold has its own price benchmarks, the Brent index is not directly related to gold prices.

Option 4: shipping rate index is also not correct. The Brent index primarily focuses on crude oil prices and does not involve shipping rates.

Therefore, option 1, crude oil prices, is the correct association for the Brent index.