The new designs of fireplaces and stoves make them more energy efficient and less polluting to the air. Which of the following has helped to made them release less exhaust and generate more heat?

1. catalytic combustor

2. internal combustion engines

3. heat pumps

4. external combustion engines

2positives of biotechnology: 1. plants have become more resistant to viruses and other communicable pests.2. with the of biotechnology, we have been able to produce better tasting fruits as well as vegetables.2 negatives of biotechnology: 1. biotechnology poses a number of environmental threats. genetically modifies crops often infect monarch butterflies and other insect species.2. viruses could combine with crops.