The correct option is: Option C: by appointing the chair and a majority of the members.
Hence, a Speaker exert power over a committee by appointing the chair and a majority of the members.
This is a very powerful position and in the United States, the Speaker is usually seen as the third most powerful politician in the country.
In fact, the Speaker is second in the line of succession after the Vice President.
The current House Speaker in the United States is Congressman Paul Ryan.