Each union elects several delegates _______ the annual conference.

• Delegate (to)
Bangla Meaning: (কাউকে) প্রতিনিধিরূপে পাঠানো; (কাউকে দায়িত্ব, অধিকার ইত্যাদি) অর্পণ করা:
English Meaning:
1) a person chosen or elected by a group to speak, vote, etc. for them, especially at a meetingto
2) to delegate somebody to attend a meeting;
3) to delegate powers to a subordinate.

• সুতরাং, শূন্যস্থানে সঠিক উত্তর হবে - to.
- Complete sentence: Each union elects several delegates to the annual conference.