The answers are B and E.

A. Intelligent: The sentence describes the cat as "apparently smart enough to spot a free lunch," which suggests a level of intelligence. However, this contradicts the idea that the cat is the "world’s least" something. So, "intelligent" is not fitting in this context.
B. Evasive: If the cat is caught several times a year by researchers, it implies that the cat is not evasive. Evasive means tending to avoid or escape from something, and since the cat is repeatedly caught, this option aligns well with the description in the sentence.
C. Fearless: Describing the cat as "fearless" would imply that it is not afraid of the researchers who catch it several times a year. However, the fact that it is caught suggests that it may not be fearless. This option doesn't fit the context.
D. Furtive: Furtive means attempting to avoid notice or attention, typically because of guilt or a belief that discovery would lead to trouble. Since the cat is caught several times a year, it indicates that it is not furtive. The cat is not successfully avoiding notice.
E. Elusive: Elusive means difficult to catch or capture. This option fits well with the context of the sentence. The fact that the researchers catch the cat several times a year suggests that the cat is easily captured, making it least "elusive."
F. Intrepid: Intrepid means fearless and adventurous. This option doesn't fit the context well because the cat is repeatedly caught, indicating it may not be particularly fearless or adventurous in this context.