Essential oils contributing to plant aroma are rich in:
Monoterpenes (C) is correct here. This is core PSS- Sec G- Sec metabolites: once you know the definition or pathway step, Monoterpenes is the clear fit. The wrong ones are A) Triterpenes; B) Phenolics; D) Alkaloids. If the topic is about gradients or potentials, water/solutes move from higher to lower of the relevant quantity.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.