Explain why the CDC recommends that everyone wash their hands for at least 20 seconds. How does this help your immune system?

Washing your hands for 20 seconds is thoroughly washing your hands. That is why the CDC recommends it. But, it necessarily doesn't help your immune system, it just keeps you safe.

Hope this answer helps you. :)

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.