One observation made by visitors is that Americans frequently prefer to answer with a brief "Yes", "No", "Sure", or the very popular "Yeah" rather than a longer reply. But brief replies do not mean Americans are impolite, rude or limited mentally. Very often, Americans are rushed and may greet you with a hurried "Hi". Indeed, this is a greeting you will hear again and again during your stay in the United States. It is used by everyone. However, those accustomed to  longer, beautifully worded phrases may need a little more time before they feel comfortable with American" plain talk".    Americans sometimes use plain talk when they are embarrassed. If people praise  them or thank them in an especially courteous way, they may be embarrassed and not know  what to say in reply.  They do not want to be impolite or rude; you can be sure that they liked  what was said about them. Except for certain holidays,  such as Christmas, Americans do not usually give gifts. Thus, you will find Americans embarrassed as they accept gifts, especially if  they have nothing to give in return. They are generally a warm but informal people! The Americans like to   _  .
answer with the words like "sure, yeah" use formal words in greeting need time to choose words in greeting get gifts from others