• 'If he helps us, we shall win': Complex Sentence.• Complex sentence:- যে sentence এ একটি Principal clause এবং এক বা একাধিক Subordinate clause থাকে, তাকে Complex sentence বলে।- Complex sentence এর subordinate clause এর শুরুতে সাধারণত if, though, although, as, because, since, so that, that, until, till, unless, when, why, who, which, where, how, before, after, whether, while বসে।যেমন:- The book that I read last night was interesting.- Even though she was tired, she stayed up late to finish her project.- If you finish your work, we can go out for dinner.অন্যদিকে,- He is both smart and kind: Compound Sentence.- I woke up early yet I was still late for work: Compound Sentence.Source: A Passage to the English Language, S. M. Zakir Hussain.