The term 'West Texas Intermediate', sometimes found in news, refers to a grade of

1. A

   Crude oil

   Crude oil. WTI is a light sweet US benchmark grade.

2. B

   Bullion

   Bullion. Gold/silver, not WTI.

3. C

   Rare earth elements

   Rare earths. Unrelated.

4. D

   Uranium

   Uranium. Unrelated.

Summary. Official key is (a). West Texas Intermediate is a grade of crude oil — the New York benchmark, beside Brent and Dubai/Oman.