Beginner Level Advanced Level
INTERMEDIATE LEVEL
Content
secret organization, secret society, underground group ☊ 
hội kín ☊
→ → →
like: hội kín → →
a closed society ☊ closed ☊
It is important to try and learn from experience. ☊ experience ☊
We think we've identified a gap in the market (= a business opportunity to make or sell sth that is not yet available). ☊ gap ☊