The correct answer is - ক) How sweet the bird is!

Affirmative থেকে Exclamatory করার নিয়ম:

• প্রথমে What (a/an) / How বসবে।

• তারপর Adjective বসবে।

• তারপর Subject + Verb বসবে।

• বাকী অংশ (যদি থাকে) বসবে।

• শেষে Note of exclamation (!) বসবে।

Examples:

• Affirmative: The bird is very sweet.
  Exclamatory: How sweet the bird is!

• Affirmative: It is a very beautiful garden.
  Exclamatory: What a beautiful garden it is!

• Affirmative: The garden is very beautiful.
  Exclamatory: How beautiful the garden is!

👉 Rule:

• যদি adjective-এর আগে a/an থাকে → What a/an ব্যবহার করতে হবে।

• যদি adjective-এর আগে a/an না থাকে → How ব্যবহার করতে হবে।

Other Options:

• খ) What sweet bird it is! → ভুল, কারণ এখানে What এর পরে a বসানো উচিত।

• গ) What the sweet bird it is! → ভুল গঠন, এখানে the হবে না।

• ঘ) How the bird is sweet! → ভুল, কারণ “How” এর পরে সরাসরি adjective আসতে হবে।

Source: Advanced Learner's English Grammar & Composition – Chowdhury & Hossain

Exclamatory Sentence: What an incredible story!
Assertive Sentence: It is a very incredible story.

Rule for converting an Exclamatory Sentence to an Assertive Sentence:

• Remove the exclamatory word (e.g., What, How) and form an assertive sentence

• Place very/most before the adjective and great before the noun if needed

• Structure: Subject + verb + a/an + very/great + adjective + rest of the sentence

More examples:

• Exclamatory: What a beautiful painting!

  • Assertive: It is a very beautiful painting.

• Exclamatory: What an excellent idea!

  • Assertive: It is a very excellent idea.

Source: