Unemployment in USA is        to remain high in 2010, and possibly for the next few years.

Experts warn that global warming will cause climate changes, including more ______ floods, heat waves and droughts. 

Smile is recognized as a/an _________ language, which can be understood by people all over     the world.

This bird is really lovely， and I’ve never seen ______ one.

 As we all know, the functions of our skin are very        .