found useful...

Can you explain the third blank please


Regards

The word should identify the idea of how the internal environment is able to survive, despite the various changes in the external environment. The only word that can match with the idea is I.

Thanks for the explanation! The word horizon got me baffled, substituting that for scope gives a lot more meaning to the whole agenda of the sentence.

i hate this kind of questions
changes can work , critical ,and preserve also
and for me they are better than the answers set by the question

Perversion has the same meaning as "deviation" as per Google. How can we conclude that deviation is the right fit for Blank 1?

I still don't understand the meaning. Please tell me how did you assume that the internal environment is mercurial and how the scope is limited?

The correct words for the blanks are (i) deviations, (ii) narrow, and (iii) perseveres.

Breakdown of the Blanks
- Blank (i): A. deviations

The first part of the sentence states that "even small...can be lethal." The word "small" is key. Deviations means a small departure from an established path or norm. This fits the context of an organism's internal environment, where a small change from the normal, balanced state can be fatal. "Perversions" is too strong and suggests a corruption, while "changes" is too general.
- Blank (ii): E. narrow

The sentence introduces a contrast with "but." Organisms can maintain a stable internal environment despite external changes. The word that describes the range of this stable internal environment must be narrow. A narrow, or tightly controlled, internal range is what allows the organism to survive. If it were "critical," that would mean it was essential, which is true but doesn't describe the range. "Intransigent" means unwilling to change, which doesn't fit the context.
- Blank (iii): I. perseveres

The final blank describes what life does in the face of "wide variations in the external environment." The word must convey the idea of continuing to exist or endure despite difficulty. Perseveres means to continue in a course of action even in the face of difficulty. This perfectly captures how life endures by maintaining a stable internal state. "Preserves" doesn't quite fit, as it's a transitive verb that requires an object (what is being preserved), and "stumbles" is a synonym for the opposite of what the sentence is trying to convey.