Cách sử dụng
The word 'sub' is often used as a shortened form of the word 'substitute'. For example, if a teacher is unable to attend a class, a substitute teacher is brought in to teach instead. This substitute teacher can be called a 'sub'. Similarly, if a person cannot attend a planned event or activity, they may ask someone else to take their place as a 'sub'. The word 'sub' can also be used as a prefix, meaning 'under' or 'below'. For instance, 'submarine' means a boat that goes below the surface of the water, and 'subway' means an underground train system.