Quite unabashed, he began his scholarly lecture on what was obvious to everyone.

Answer: Option A

Unashamed : expressed or acting openly and without guilt or embarrassment.
Unimpressed : feeling no admiration, interest, or respect.
Unnerved : make (someone) lose courage or confidence.
Unchecked : (especially of something undesirable) not controlled or restrained.
Unabashed : not embarrassed, disconcerted, or ashamed.

Synonym of Unabashed is Unashamed