Answer:
I believe it is the act of being solicitous.
Step-by-step explanation:
The suffix -tude represents a state or condition while solicitous means "to express concern". While "characterized by being solicitous" could have been an answer, at the same time it does not make sense with the root word being solicitous. Characterize means "to describe the distinct nature of", or "be typical or characteristic of". Therefore, the act of being solicitous seems to be the correct option.