SAT Inferences Question

There are over 150 species of the cactus genus Mammillaria throughout the Americas, but their survival can be threatened by high precipitation and dense vegetation that blocks sunlight. Researchers have located species from the genus in almost every state in Mexico, with several of them, like M. knippeliana, restricted to only one state. The fact that this genus has not been observed in eastern and western Coahuila has been attributed to a lack of appropriate habitat, but much of the landscape in this area is notoriously inaccessible, which suggests that Which choice most logically completes the text?