Which sentence is the correct one?

His is an indomitable mind.
Double Possessive হিসেবে এখানে his বলতে his mind বুঝাচ্ছে। অর্থাৎ- His mind is an indomitable mind.
যেমন আমরা বলি Ours is a beautiful country. অর্থাৎ- Our country is a beautiful country.

অন্যান্য গুলোর সঠিক বাক্য হবে:
ক) One should do one’s duty.
খ) These movies have lost their appeal now-a-days.
গ) Everyone should respect his teacher / his or her teacher.