a.

Famous caves in Viet Nam: (Một số động nổi tiếng của Việt Nam)

• Phong Nha Cave
• En Cave (hang Én)
• Sung Sot Cave (hang Sửng Sốt)
• Tam Coc - Bich Dong (Ninh Binh)

Famous caves in the world: (Một số động nổi tiếng trên thế giới)

• Deer Cave (Borneo, Malaysia)
• Onondaga Cave (Missouri, USA)
• Gouffre Berger Cave (France)
• Reed Flute Cave (Guilin, China)
• Fingal's Cave (Scotland),
• Cave of Crystals (Mexico)

b.

1. Where is Son Doong Cave located? 
   => Son Doong is located in Quang Binh Province, Viet Nam. 
2. When was it discovered? 
   => It was discovered in the end of 20^th century. 
3. How long is the cave? 
   => The cave is nearly 9 kilometers in length. 

a.

Famous caves in Viet Nam:

- Phong Nha Cave

- En Cave 

- Sung Sot Cave 

- Tam Coc - Bich Dong (Ninh Binh)

Famous caves in the world:

- Deer Cave (Borneo, Malaysia)

- Onondaga Cave (Missouri, USA)

- Gouffre Berger Cave (France)

- Reed Flute Cave (Guilin, China)

- Fingal's Cave (Scotland),

- Cave of Crystals (Mexico)

b.

1. Son Doong is located in Quang Binh Province, Viet Nam. 
2. It was discovered in the end of 20^th century. 

3. The cave is nearly 9 kilometers in length.