Two scientists test soil fertility in a forest and a nearby field. both scientists find that the soil fertility in the forest is higher than the soil fertility in the field. scientist a says that the forest's soil fertility is higher because the forest has more vegetation that keeps the topsoil from eroding. scientist b says that the forest's soil fertility is higher because the forest's soil has a high count of decomposing bacteria. which of the scientists' conclusions is valid?
neither scientist's conclusion is valid because soil fertility is hard to test.
only scientist a's is valid because it is supported by evidence.
only scientist b's is valid because bacteria increase soil fertility.
both scientists' conclusions could be valid.