A hydrologist is studying the effects of living environments on the life span of fish in different bodies of water. The hydrologist considers two factors: pH level and prevalence of a certain acidic compound. The hydrologist exposes fish to one of the following types of water environments.

water with a pH higher than 7, and more than 70 parts per trillion of a certain acidic compound
water with a pH lower than 7, and more than 70 parts per trillion of a certain acidic compound
water with a pH higher than 7, and less than 70 parts per trillion of a certain acidic compound
water with a pH lower than 7, and less than 70 parts per trillion of a certain acidic compound
Each of these four environments is an example of a [blank] for this experiment.

Which word correctly fills in the blank in the previous sentence?
statistic
treatment
parameter
population

Whats you answers ? And can you add number so Ik which problem?

A hydrologist is studying the effects of living environments on the life span of fish in different bodies of water. The hydrologist considers two factors: pH level and prevalence of a certain acidic compound. The hydrologist exposes fish to one of the following types of water environments.

water with a pH higher than 7, and more than 70 parts per trillion of a certain acidic compound
water with a pH lower than 7, and more than 70 parts per trillion of a certain acidic compound
water with a pH higher than 7, and less than 70 parts per trillion of a certain acidic compound
water with a pH lower than 7, and less than 70 parts per trillion of a certain acidic compound
Each of these four environments is an example of a [blank] for this experiment.

Which word correctly fills in the blank in the previous sentence?

This part is the question.

Which word correctly fills in the blank in the previous sentence?

a) statistic
b) treatment
c) parameter
d) population

The correct word to fill in the blank in the previous sentence is "treatment". Each of these four environments (water conditions) is being considered as a treatment in this experiment.