Had I know his true intentions, I→would had never alllowed him to come.
Had I know his true intentions, I→would had never alllowed him to come. Correct Answer would have never allowed
Had I known = If I had known. সুতরাং এরপর would have + v_3 বসবে। If যুক্ত অংশে Past Perfect Tense হলে পরের অংশ would have done বা would have allowed বসে। সুতরাং সঠিক উত্তর (b)।