Here are the best options to fill in the blanks:

1. (1) **from**
2. (2) **occasion**
3. (3) **traditional**
4. (4) **ingredients**
5. (5) **because**

So the completed text would read:

"My name is Nam, and I'm from Vietnam. The Lunar New Year, or Tet, is our country's biggest festival. This special occasion often falls between late January and early February. At Tet, our family gather and make Banh Chung, a traditional food. We need to prepare lots of ingredients such as pork, sticky rice, and mung bean. We also clean and decorate our house before Tet. I like Tet so much because it is the time for family gatherings."