D. the - a
Explanation: "Tet" is a specific holiday, so it requires "the," and "lunisolar calendar" refers to a type of calendar in general, so "a" is used.

B. a - x
Explanation: "Opportunity" is used as a countable noun, so "a" is appropriate. "Gods of harvest" is a general reference, so no article is used before "gods."

B. a - the
Explanation: "Inevitable part" requires "a" (since it is a singular, countable noun), and "gifts" refers to specific gifts, so "the" is used.

A. The - an - a
Explanation: "The Khmer people" refers to a specific group, so "the" is used. "An indigenous ethnic minority" uses "an" because it starts with a vowel sound. "A long history" uses "a" because it is a singular countable noun.

A. The - x
Explanation: "The O Du's culture" refers to a specific culture, so "the" is used. "Nghe An province" doesn't need an article before "Nghe An."

D. The - an
Explanation: "The National Village for Ethnic Culture" refers to a specific place, so "the" is used. "An excellent place" is a singular countable noun, so "an" is used.

A. the - a - the
Explanation: "The family" refers to a specific family, "a first day" refers to the first day in a general sense, and "the entire following year" refers to the specific year after the first day.

D. The - the - the
Explanation: "The values" refers to specific values, and "the Mong people's traditions" refers to traditions of a specific group, so "the" is used throughout.

A. a - the
Explanation: "A symbol" because it refers to one of many possible symbols, and "the important clothing accessory" because it refers to a specific accessory.

C. x - the - x
Explanation: "Evident gap" doesn’t need an article, "the deltas" refers to specific delta regions, and "mountain areas" is a general reference, so no article is used.