That is exactly what I was looking for ; the examples are really good. Thanks a lot for that and thanks everyone for the responses.From the question, it seems that kalpab has looked up the words (there is a contrast in meaning between "belie" and "betray") and needs some help:
Belie: to hide (a true situation). Her wisdom belies her young age.
Betray: to reveal (a true situation): His inappropriate response betrayed his inexperience.