Given the task definition and input, reply with output. In this task, you're given a question, a context passage, and four options which are terms from the passage. After reading a passage, you will get a brief understanding of the terms. Your job is to determine by searching and reading further information of which term you can answer the question. Indicate your choice as 'a', 'b', 'c', or 'd'. If you think more than one option is plausible, choose the more probable option to help you answer the question.

Question: How tall is the mountain range that Muleshoe is at the foot of? Passage:Muleshoe is situated on the Great Plains in an area where the plains reach their highest altitude at the foot of the Rocky Mountains known as the High Plains; more specifically, it is located on the South Plains in a region known as the Llano Estacado. The area topology is gently rolling plains with a large number of playa lakes on top of a large plateau. Many of the playa lakes have dried out due to the water exploitation of the Ogallala Aquifer that helped supply water to the lakes during dry seasons. Soil types vary from dark brown playa-lake silt to iron-rich clay to sandy soil; topsoil and subsoil layers vary, as well. Most of the area contains a layer of caliche; in some areas, no topsoil or subsoil reveals the layer of caliche, while other places have up to 4 ft of topsoil or subsoil combined.
Links: a. Rocky Mountains b. Rocky Mountains c. Caliche d. Rocky Mountains
a