Concept:
The word extempore refers to speaking or performing without prior preparation. It is spontaneous and improvised.
Step 1: Understand the meaning of extempore.
\[
\text{Extempore} = \text{without preparation}
\]
For example:
\[
\text{"She delivered an extempore speech."}
\]
This means the speech was given without advance planning.
Step 2: Determine the opposite meaning.
The opposite of acting without preparation is being thoroughly prepared beforehand.
Step 3: Analyze the options.
• Well-prepared -- carefully planned and prepared.
• Careful -- attentive but not necessarily prepared.
• Extraordinary -- remarkable.
• Unprepared -- nearly the same meaning as extempore.
Step 4: Select the antonym.
Therefore, the antonym of extempore is well-prepared.
\[
\boxed{\text{Well-prepared}}
\]