Final answer:
The headline that suggests a positive bias toward the subject matter is 'Congress gains momentum on environmental progress.'
Step-by-step explanation:
The headline that suggests a positive bias toward the subject matter is 'Congress gains momentum on environmental progress.' This headline implies that Congress is making progress in addressing environmental issues, which is seen as a positive development. It gives the impression that Congress is actively working towards improving the environment, which can be viewed positively by people who are concerned about environmental issues.