Adirect indication that the white blood cells of the body are functioning would be what

Which event would lead to primary succession of a forest?

What substance acts to prevent sudden ph changes in bodily fluids?

Ihave no idea how to solve these. plus there's another question that is 2) a 10 kilogram meteorite is collected in space and brought back to earth. it is composed of 1.25 kg of uranium-238 and 8.75 kg of lead-206. how many u-238 half lives have passed? what is the approximate age of the meteorite?