Final answer:
People can train themselves to identify frog calls by actively listening to the sounds made by frogs during their spring mating season.
Step-by-step explanation:
The line 'Each spring, these volunteers stand quietly along stretches of the country's roads, listening to frogs' best supports the idea that people can train themselves to identify frog calls. By actively listening to the sounds made by frogs during their spring mating season, volunteers can become familiar with the unique calls of different frog species. Over time, they can develop the ability to identify these calls and contribute to a frog census.
Learn more about Frog calls