Here's a suggested completion for the sentences in your text:

The Vietnamese are known to be polite, **(1) open** and sensitive. They have a casual and friendly manner. They regard friendship as being very important throughout one's life. They are always **(2) hospitable** to visits from friends. Drop-in visits are welcome. The Vietnamese are very close to their family. When they offer you a gift, the Vietnamese will usually **(3) speak** lightly about it. Even though it is an expensive gift, they may pretend it is of no great monetary value. With **(4) 4,000** years of civilization, the Vietnamese are proud people who like to recite to a **(5) myth** that they are descendants of an angel and a dragon.