| 摘要 |
<p>A protective cover for document files is made from a sheet of strong paper, thin cardboard or sheet metal. The sheet is folded in the middle and perforated along opposite edges. Alternatively, instead of a central fold the cover may be made from two sheets joined by a strip of flexible foil. Another form of cover is made from one sheet with a souble fold and with holes along the edge of the lower part of the cover which adjoins the fold line.</p> |
