Concept:Gummosis is a plant disease whose most defining symptom is the exudation of gum from affected plant parts.
Explanation:Yellowing of leaves and drying up of leaves indicate stress caused by infection.
Raised brown spots on the leaves also appear as the infection progresses.
However, the exudation of gum is the most distinctive symptom among the listed signs.
This combination of symptoms, especially gum exudation, is characteristic of gummosis.
It is not die-back, tristeza, or blight because those diseases do not typically show gum exudation as a primary symptom.
Answer:B. gummosis