vẫn trong vòng bí ẩn 
still unknown, remain a mystery [ vẫn ] : still, yet
[ trong ] : during; in(side), among
[ vòng ] : circle, ring, round
[ bí ] : (1) pumpkin, squash; (2) fine-toothed; (3) secret, mysterious; (4) obstructed, constipated, blocked, stumped
[ ẩn ] : to hide, take shelter; hidden, concealed
Most Common Compounds Set 1:
Most Common Compounds Set 2 :