Question

low energy waves are radio waves. their length may be as long as... a hydrogen atom the universe a bacteria an asteroid

Explanation:

The image shows that radio waves can be up to 100 kilometers in diameter. An asteroid (the one that killed the dinosaurs) is in the range of kilometers in size. A hydrogen atom is extremely small (on the order of picometers), bacteria are micrometers - millimeters in size, and the universe is vast (light - years).

Answer:

an asteroid