Here are the best options for each numbered blank based on the context of the passage:

36. **A. minority** - "ethnic minority groups like the Tay, the Hmong"
37. **C. watching** - "hence, on the market days, there are quite bustling watching trade activities"
38. **A. put on** - "specialties including corn wine, soy bean as well as five-colour sticky rice. It's also a special occasion for the ethnic people to put on nice colourful clothes"
39. **B. wear** - "dressed in nice colourful clothes woven by skilled women"
40. **C. many** - "exciting cultural events also happen at the fairs to serve the locals and tourists."

So the completed passage would read:

Hill tribal markets are a distinctive feature in northern mountainous provinces in Viet Nam. Every year, these unique markets attract millions of holidaymakers who love finding out the culture of ethnic **minority** (36) groups like the Tay, the Hmong, etc. Most flea markets take place once a week, from early morning till noon due to the inconvenience of long distances between neighboring communities. Hence, on the market days, there are quite bustling **watching** (37) trade activities. Visitors can **put on** (38) a lot of local specialties including corn wine, soy bean as well as five-colour sticky rice. It's also a special occasion for the ethnic people to **wear** (39) nice colour clothes woven by skilled women, which motivates tourists to purchase brocade products for their own use. What's more, **many** (40) exciting cultural events also happen at the fairs to serve the locals and tourists.