GKFix MCQ Question

In telescope formulas, what do fₒ and fₑ usually represent?

• A. fₒ: Eyepiece focal length; fₑ: Objective focal length.
• B. fₒ: Objective diameter; fₑ: Eyepiece diameter.
• C. fₒ: Telescope length; fₑ: Eyepiece length.
• D. fₒ: Objective focal length; fₑ: Eyepiece focal length.