Which of the following words is in singular form?

✅ কেন সঠিক: ‘Radius’ is singular; its plural is ‘radii’. So ‘radius’ is the singular form.

❌ অন্য অপশন: Formulae (plural of formula), agenda (originally plural of agendum) and oases (plural of oasis) are plural forms.

💡 মনে রাখুন: Latin -us → -i: radius → radii, focus → foci; -is → -es: oasis → oases.

📖 শব্দার্থ: radius = ব্যাসার্ধ; formula = সূত্র; oasis = মরূদ্যান; agenda = আলোচ্যসূচি।