He tried his best but could not pass the written exam. Here 'but' is-

He tried his best but could not pass the written exam.Here 'but' is a conjunction.• Compound sentence এর দুইটি clause কে and, but, or, yet ইত্যাদি conjunction দ্বারা যুক্ত করতে হয়। The word 'but' is used here to connect two clauses:এই Compound Sentence এ দুইটি Clause হলো-- "He tried his best"এবং- "could not pass the written exam"এই দুইটি Clause কে but সংযুক্ত করে এবং বিপরীত ভাব প্রকাশ করে। Conjunction: A conjunction is a part of speech that connects two or more words, phrase, clause or sentence. - Conjunction হলো একটি part of speech যা দুই বা ততোধিক words, phrase, clause বা sentence কে যুক্ত করে। - যেমন: but, or, and. Source: A Passage to the English Language by S.M. Zakir Hussain.