The disease cycle which represents the height of the disease and characterised by clear-cut signs and symptoms is:

Correct option is C

The fastigium stage in the disease cycle is the period where the disease reaches its peak severity. Symptoms are most evident and distinct during this time, aiding diagnosis. After this phase, either recovery (convalescence) or deterioration may follow, depending on disease and treatment effectiveness.
Explanation of options: (a) ✘ Convalescence – Recovery phase when symptoms gradually resolve. (b) ✘ Defervescence – Phase when fever begins to decline, not necessarily peak illness. (c) ✔ Fastigium – Represents the peak stage of the disease with maximal symptoms. (d) ✘ Defection – Not a clinical term used in disease progression stages.