Concept:
Professional commitment is the dedication of a teacher to improve teaching practices through self-motivation rather than external rewards or pressure.
Step 1: Understand the situation.
The teacher improves lesson plans voluntarily, indicating intrinsic motivation and commitment to professional growth.
Step 2: Analyse the options.
• Administrative compulsions -- No external compulsion is mentioned.
• Institutional pressure -- The question states there is no outside pressure.
• Aiming for cent percent results -- Not necessarily indicated.
• A strong inner sense of professional commitment -- Correct. \checkmark
Step 3: Final conclusion.
Therefore, the teacher demonstrates
\[
\boxed{\text{A strong inner sense of professional commitment}.}
\]