Which material typically make up the a horizon in soil

The excretory system,need answers for all: )

To calculate percent by mass, use the equation below: calculate the percent by mass of each element. %n = % %h = % %o = %

Ascientist conducted an experiment and discovered that certain plants grow faster when given a particular amount of fertilizer. anouther scientist conducted the same experiment and got similar results. which concept does this best illustrate? a) repetition b) replication c) precision d) validity