Ecologists often use modeling, instead of field studies, because it

a. allows them to control all of the variables involved.
b. them collect more samples.
c. is less expensive than working in the field.
d. lets them study many organisms at once.

Answer is A. allow them to control all the variables involved.

Explanation:

Modelling in ecology means the use of constructed mathematical models for understanding of ecological processes and to predict or know how real it is for ecosystem to change.

Ecological modelling is useful in defining problems more precisely and clarity of concepts.