The answer is ‘remain’.
When we consider the relationship between the terms, ‘passive’ often implies a state of being influenced by external factors, leading to a change. In contrast, ‘active’ suggests taking initiative or control, often indicating a state of stability or continuity. Therefore, while ‘passive’ changes, ‘active’ tends to remain more consistent or unaffected, standing in its own agency. This creates a parallel structure where both terms illustrate different approaches to engagement and influence.