reactive
adjective /riˈæktɪv/
  /riˈæktɪv/
 - (formal) showing a reaction or response反应的;有反应的;回应的 - The police presented a reactive rather than preventive strategy against crime.警方对付犯罪的办法,不是事先加以防范,而是事后作出反应。 
 
- The police presented a reactive rather than preventive strategy against crime.
- (chemistry化学 能起化学反应的;易反应的 - highly reactive substances很容易起反应的物质 
 
- highly reactive substances