"Though he is rich, he is polite." - This sentence is an example of -

♦ 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।

সুতরাং, নিয়মানুযায়ী - Though he is rich, he is polite. হচ্ছে complex sentence.