The sentence contrasts his remarks with the audience's reaction. This implies that his remarks might have been negative, yet his ideas were interesting. "Derisive" means mocking or contemptuous, which fits this contrast.
Explanation of other options:
- "Laudatory" means expressing praise — inconsistent with contrast.
- "Euphemistic" refers to mild or indirect language — doesn't imply negativity.
- "Succinct" means brief and to the point — does not express contrast.