câu hỏi then chốt 
important question [ câu ] : (1) phrase, expression, sentence; (2) to fish, go fishing
[ hỏi ] : (1) to ask, inquire, question; (2) low-rising tone
[ then ] : latch (of a door)
[ chốt ] : axle, bolt, pin, key, latch, wedge, dowel
Most Common Compounds Set 1:
Most Common Compounds Set 2 :