Concept:
A web document is a document that can be displayed in a web browser. Web pages are mainly created using HTML.
Step 1: Understand HTML.
HTML stands for:
\[
\text{HyperText Markup Language}
\]
It is used to structure content on web pages such as headings, paragraphs, tables, links, images, and forms.
Step 2: Check FTP.
FTP stands for File Transfer Protocol. It is used to transfer files from one system to another, not to create web documents.
Step 3: Check GPL.
GPL stands for General Public License. It is a software license, not a language for creating web documents.
Step 4: Check HTML.
HTML is the correct tool/language used to create web documents.
\[
\text{Web document} \rightarrow \text{HTML}
\]
\[
\therefore \text{Correct Answer is (D)}
\]