Toby's class is learning how different kinds of pollution affect living organisms. one of the things he has learned is that chemicals, such as laundry detergent, that we put down our drains can end up in lakes, rivers in streams.

toby decides to use what he has learned to set up an experiment to determine whether some kinds of laundry detergents are more harmful to plants than others. in his experiment, toby will make four terrariums from soda bottles. he will put soil in the bottom of the terrariums and put a plant in each one.

which of the following tables correctly shows which variables toby should keep the same in his experiment and which variables he should change?

w.
x.

y.
z.
a.
z
b.
w
c.
x
d.
y
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