The sentence that contains the most reasonable inference and provides a valid clue to support it is:
"The hotel clerk does not know the Spanish word for men."
The clue that supports this inference is:
"Not knowing what they meant we asked the clerk, who explained that when the sign said M-E-N it was for me."
This indicates that the hotel clerk lacks familiarity with the Spanish language, which implies a language barrier and can lead to the inference that he might not be proficient in Spanish. The explanation he gives suggests that he only understands the English word "men" and has difficulty with the corresponding Spanish term, supporting the idea that the hotel clerk does not know the Spanish word for men.