Which gesture suggests nervousness?
burying your head in your hands
leaning back in your chair
biting your nails
pounding your fists

Option (c) is the correct answer.

Explanation:

Nervousness is a feeling of getting worried about something or showing anxiety over something.

For example, a student giving speech in front of whole school felt nervous and forgot lines from his speech.

Therefore, nervousness can make a person forget content that he has prepared to deliver.

Some signs of being nervous are sweating, biting nails, shaking of hands etc.

Thus, we can conclude that out of the given options, biting your nails is a  gesture that suggests nervousness.

what experimental evidence led scientists to change from the previous model to this one?

a few of the positive particles aimed at a gold foil seemed to bounce back.

the colors of light emitted from heated atoms had very specific energies.

experiments with water vapor showed that elements combine in specific proportions.

cathode rays were bent in the same way whenever a magnet was brought near them.