Pedro thinks that if he adds earthworms to a compost pile, it will decompose twice as fast as a compost pile without earthworms. pedro has designed an experiment to test his prediction. the steps of his experiment are shown below.

start two compost piles at the same time with the same materials.

add earthworms to one compost pile.

add fungi to the other compost pile.

judge the level of decomposition in each compost pile every week.

report the results.
which step in pedro's experiment would make it difficult for pedro to fairly compare the two compost piles?
a.
step 3
b.
step 1
c.
step 4
d.
step 2
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