a rolltop desk的用法和样例：
- Ralph and his brother, Herbert, were supplied with chemistry sets, toy typewriters, and a rolltop desk so that they would have the tools to succeed.
- Good writers are not only the privileged few who read nothing but Tolstoy and sit on specially designed chairs in front of rolltop desks with pigeon holes and inkwells.
- The large box in his room can serve as a desk too.
- The desk calculator use a roll of paper.
- Look! There's a big cockroach on your desk light.