Important rock-and-roll artists and groups in the 1990s and early 21st century included which of the following? A. The Four Seasons B. The Beatles C. Radiohead D. None of the above

The correct answer is C. Radiohead.<br /><br />Radiohead is a British rock band that formed in 1985 and became one of the most influential and critically acclaimed bands of the 1990s and early 21st century. They are known for their experimental and avant-garde approach to rock music, incorporating elements of electronic, ambient, and classical music into their sound.<br /><br />The other options, The Four Seasons and The Beatles, are not correct. The Four Seasons is an American rock and pop band that was active in the 1960s, while The Beatles were a British rock band that was active in the 1960s. Neither of these bands were active or influential during the 1990s and early 21st century, which is the time period specified in the question.