Is a chemical substance that is produced in substantial quantities, and is reasonably expected to be released in to the environment in substantial quantities a risk trigger, standard trigger, or an exposer trigger? Means that the EPA has made a determination that a chemical or biological agent may present an unreasonable risk both in toxicity and exposure.
a. exposer trigger
b. standard trigger
c. risk trigger

c-risk trigger

Explanation:

The Risk Evaluation process is the second step, following Prioritization and before Risk Management, in EPA’s existing chemical process under TSCA.  The purpose of risk evaluation is to determine whether a chemical substance presents an unreasonable risk to health or the environment, under the conditions of use, including an unreasonable risk to a relevant potentially exposed or susceptible subpopulation.  As part of this process, EPA must evaluate both hazard and exposure, exclude consideration of costs or other non-risk factors, use scientific information and approaches in a manner that is consistent with the requirements in TSCA for the best available science, and ensure decisions are based on the weight-of-scientific-evidence. 

hi~~

i would say that hybridization occurs frequently in nature, because there are many types of hybrids that have occurred naturally, such as the mule (male donkey + female horse)