20. which activity is an example of a chemical change?
(1) dissolving table salt in water
(3) hammering aluminum into thin sheets
(2) melting gold to make jewelry (4) burning wood to produce ashes

Some birds look for food near cattle and other livestock. the movement of the cattle churns up the ground, making insects available to the birds. the cattle appear to be unaffected by the presence of the birds. what kind of relationship exists between the birds and the cattle? o a. parasitism o b. commensalism o c. predation o d. mutualism

What percentage of light hits earth's surface directly?

Awave has a wavelength of 15 mm and a frequency of 6 hertz. what is its speed?