(a) Crude oil     

(b) Bullion     

(c) Rare earth elements     

(d) Uranium

Answer: a

Explanation:

West Texas Intermediate (WTI) is a type of crude oil that serves as one of the primary benchmarks for oil pricing, alongside Brent and Dubai Crude. Known for its high quality, WTI is relatively easy to refine, making it a popular choice in the oil market.

Hence, option a is correct.

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