Final answer:
The word potent means 'producing a strong effect' and is the correct answer among the provided options.
Step-by-step explanation:
The word that means "producing a strong effect" is b. Potent. To define the terms given: Overt means open and observable; not hidden or secret. Potent refers to something that has great power, influence, or effect. Ominous suggests that something bad or unpleasant is going to happen. Lastly, Insidious describes something that proceeds in a gradual, subtle way, but with harmful effects.