They appointed him president. (passive)

The correct answer is - খ) He was appointed president by them.

Transitive verb-এর পরের complement (যেমন secretary, captain, president ইত্যাদি) active ও passive দুই voice-এই complement থাকে, subject হিসেবে ব্যবহৃত হতে পারে না।
যেমনঃ
- Active: We elected him secretary
- Passive: He was elected secretary by us.
- (Incorrect): Secretary was elected he by us.

Other options:
ক) President was appointed him by them.
বাক্য গঠনের ভুল: "President" কে subject করা ঠিক নয়, এবং “him” এর অবস্থানও ভুল।

গ) He appointed president by them.
“appointed” এর আগে auxiliary verb “was” নেই, এবং structure ভুল।

ঘ) President was him appointed by them.
শব্দগুলোর ক্রম সম্পূর্ণভাবে বিভ্রান্তিকর এবং grammar ভুল।

Source: A Passage to the English Language by S M Zakir Hussain.