Correct option is A
Given:
Painting → brush, Letter → ?
Painting → Brush (Brush is the tool for painting) Painting is an activity that requires a Brush as a tool.
Check each options:
A) Letter → Pen (Pen is the tool for writing a letter) Letter is an activity or item that requires a Pen to be written.
B) Writer: A writer is the person who writes a letter, but the tool for writing a letter is a pen, not a person.
C) Ink: Ink is used in a pen, but the direct tool for writing a letter is the pen itself.
D) Post-Office: The post-office is where letters are sent, but it's not the tool used for writing a letter.
So, Pen is the appropriate choice to complete the analogy.
Thus, the correct option is: (a)