Do Vietnamese ___________________ often eat moon cakes at the Mid-Autumn Festival?
Answer: B. people
Explanation: "People" is the correct term when referring to a group of individuals from a particular nationality or culture.

Among mountainous regions in Viet Nam, _________________ one will you want to travel to?
Answer: D. which
Explanation: "Which" is used when asking about a specific item or choice from a known set, in this case, the regions.