Select the most appropriate option to fill in the blank.
Thank you for your ______ to speak at the conference in March.

Correct option is C

The correct option to fill in the blank is (c) invitation.
Explanation:
The sentence expresses gratitude for the opportunity to speak at a conference, which is best associated with an invitation.
So, the correct sentence is:
Thank you for your invitation to speak at the conference in March.
Word Meaning:
Invitation: a written or spoken request to attend or participate in an event (निमंत्रण)
Example:
I received an invitation to attend the award ceremony.
Other
· (a) Conclusion: the end or finish (समाप्ति)
· (b) Inclusion: the act of being part of something (शामिल करना)
· (d) Introduction: the act of presenting someone or something (परिचय)
None of the other options logically fit the context of being thanked for an opportunity.