What is the main substance to need every planet, star , for his gravity

The diagram shows a boulder rolling down a hill into a valley and then up the opposite hill. at which position does the boulder have the greatest kinetic energy? ab c d

Why do atoms emit energy of only specific wavelengths

Answer asap 50 points which of the following illustrates how a venus fly trap senses that an insect has landed in its open leaves? 1. using tiny hairs, the leaves sense a change in light. 2. using tiny hairs, the leaves taste a chemical. 3. using tiny hairs, the leaves detect a touch. 4. using tiny hairs, the leaves sense a change in water levels.