Rajshahi is one of the oldest cities in Bangladesh. (Make it a positive degree)

Correct answer: Very few cities in Bangladesh are as old as Rajshahi.

Superlative: Rajshahi is one of the oldest cities in Bangladesh.
Positive: Very few cities in Bangladesh are as old as Rajshahi.

• One of the যুক্ত Superlative Degree কে Positive Degree করার নিয়ম:
প্রথমে Very few বসে।
তারপর Superlative Adjective-এর পর থেকে বাকি অংশ বসে।
Verb-এর plural form বসবে।
As/So + Superlative Adjective-এর positive form + As বসে।
প্রদত্ত sentence-এর subject শেষে বসে।

Other Options:
ক) No other city is as old as Rajshahi in Bangladesh.
- এটি ভুল, কারণ one of the যুক্ত Superlative Degree কে Positive Degree করার ক্ষেত্রে প্রথমে Very few বসে।

খ) Very few city is as old as Rajshahi in Bangladesh.
- এটি ভুল, কারণ Very few-এর পরে plural noun এবং plural verb বসে। তাই “city is” নয়, “cities are” হবে।

গ) No other cities are as old as Rajshahi in Bangladesh.
- এটি ভুল, কারণ one of the যুক্ত Superlative Degree কে Positive Degree করার ক্ষেত্রে No other নয়, Very few বসে।

Source:
Advanced Learner's Communicative English Grammar & Composition by Chowdhury & Hossain.
Website English Wizard