Margin lines are . . . . . . . . in colour.

The correct answer is: D. Black

Margin lines are typically black in color. They are used to separate the text from the edge of the page. They can also be used to indicate the margins of a document.

Option A: Blue is not a common color for margin lines. It is more common to see blue used for headings or other elements that are meant to stand out.

Option B: Red is also not a common color for margin lines. It is more common to see red used for warnings or other elements that are meant to grab attention.

Option C: Green is not a common color for margin lines. It is more common to see green used for highlighting or other elements that are meant to be visually appealing.