Answer:
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.
The answer is B. Hydrogen Bonds
The Miller-Urey experiment showed that simple molecules could have arisen abiotically. This chemical experiment included conditions similar to those present on the early Earth, and tested the origin of life under those conditions.
Water (H2O), methane (CH4), ammonia (NH3) and hydrogen (H2) were the chemicals used to produce the results of the experiment, the factors needed for simple life to arise. Given similar conditions on other planets, it's possible that life could arise there as well.
Http://www.healthline.com/health-slideshow/home-remedies-for-head-lice#1
This may help :)