Problem: Tom and Andy are two old friends. Tom was infected with HIV 20 years ago, and Andy has been helping him ever since. Andy is as healthy as an ox. Which friend has a weaker immune system?

A: Tom

Problem: Two students studied the atmosphere of Earth and other planets from our solar system. Zack learned about Earth's atmosphere, while Ken learned about the atmospheric conditions on planet Venus. Which student learned less about carbon dioxide clouds?

A: Zack

Problem: To reenact James Watt's experiment, John sealed some water in a container. He called this stage of his experiment as stage A. Then he started heating the water in the sealed container. He labeled this stage as stage B. Once the temperature reached hundred degree centigrade, he added more heat to it. He called this stage as stage C. Once all the water has turned into steam, he kept adding heat to it. He called this last stage of is experiment as stage D. In which stage the water would have less kinetic energy, stage A or stage B?

A: stage A

Problem: Danny started weight lifting two years ago, he wanted to be bigger. His brother Arnie preferred athletic competitions such as running, so he became a runner. Which brother gradually increased the size of his muscles?

A:
Danny