Select the most appropriate option that can substitute the underlined segment in the given sentence.
The author’s writing style is characterised by its poetic language.

The correct option is lyrical language.

Explanation:

The word "poetic" refers to qualities that are expressive, romantic, imaginative, or characteristic of poetry, often having a musical rhythm or rhyme.

Let's analyze the given options to find the best substitute:

1. Lyrical language: "Lyrical" means expressing feelings and thoughts in a beautiful, poetic, or song-like manner. Therefore, "lyrical language" is the closest synonym to "poetic language".
2. Simple language: Means easy to understand or basic, which does not capture the poetic quality.
3. Lucid language: Means clear, transparent, or easily understood, which does not necessarily imply poetic quality.
4. Prosaic language: Means mundane, ordinary, or lacking poetic beauty (in fact, it is the antonym of poetic).

Thus, substituting "poetic language" with lyrical language maintains the original meaning of the sentence perfectly.