—I have been waiting for you so long. —Sorry, I have been in the library, _______ my friend look for some books.
The president spoke at the business meeting for nearly an hour without ___ his notes.
He is really an excellent doctor and he is _____ to becoming an expert in this field.
He is such a strong-willed person that there is nothing in the world that can _____ him.
Come and see me whenever ____.
As we can see, the prices of vegetables _____ according to the season.