The correct answer is - গ) This book is very interesting.

• Adverb of degree:
- এই ধরনের adverb কতোখানি, কি মাত্রায় এসব বোঝায়।
- It tells us about the intensity of something.
- Example: Almost, quite, very, much, fully, partly, wholly, completely, strongly, totally, entirely, deeply, greatly, poorly, half, enough, somewhat, altogether, too, little, a little, rather.
- Example Sentence: The water is quite cold.

• Adverb:
- Adverb হলো এমন একটি শব্দ যা verb (ক্রিয়া), adjective (বিশেষণ) অথবা অন্য adverb (ক্রিয়া বিশেষণ)-কে modify বা বিশেষিত করে।

• Adverb of manner:
- যে adverb কোনো কিছু কিভাবে হয় হচ্ছে তা উল্লেখ করে তাকে Adverb of manner বলে।
- Example: sadly, softly, steadily, slowly, soundly, swiftly, simply, suddenly, carefully, carelessly, easily, quickly, possibly, probably, luckily, fortunately, unfortunately, naturally, rightly, urgently, wrongly.
- Example Sentence: He spoke quickly during the meeting.

• Adverb of time:
- এই ধরনের Adverb যে গুলো ক্রিয়া সম্পন্ন হওয়ার সময় বুঝায়। এটি সাধারণত When কখন দিয়ে প্রশ্ন করলে উত্তর দেয়।
- Example: Now, then, before, since, ago, already, once, twice, thrice, again, soon, late, afterwards, yesterday, today, tomorrow, daily. early, formerly, frequently, presently, immediately, instantly.
- Example Sentence: They arrived yesterday at the station.

• Adverb of frequency:
- যে Adverb কোন কিছু করার বা কতো সময় পরপর হয় তা বোঝায় তাকে Adverb of frequency বলে।
- Some Adverb of frequency: always, usually, often, sometimes, rarely, never etc.
- Example Sentence: He never lies to his friends.

• Other options
ক) He spoke softly during the meeting.
'Softly' হলো Adverb of Manner - কিভাবে কথা বলেছে তা বোঝায়।

খ) They often visit us.
'Often' হলো Adverb of Frequency - কত ঘন ঘন আসে তা বোঝায়।

ঘ) I saw her yesterday.
'Yesterday' হলো Adverb of Time - কখন দেখা হয়েছে তা বোঝায়।

Source: Applied English Grammar and Composition by P. C. DAS.