Final answer:
The question likely relates to electric fields in Physics. It suggests a response of S2 to S1, which could either be 'positive' or 'negative' based on the nature of the charges involved, with 'positive' indicating attraction and 'negative' indicating repulsion between S1 and S2.
Step-by-step explanation:
The question seems to be pertaining to the concept of electric fields in Physics, specifically how they are related to electric charges. However, the question is not entirely clear in its context, potentially missing some detail or background for a definitive answer. Based on the information provided that the 'number of field lines leaving a positive charge or entering a negative charge is proportional to the magnitude of the charge', we can derive that when S2 receives from S1, if they are charges, it may exhibit either an attraction or repulsion.
These interactions could be described as either positive or negative responses in the context of electric fields. Positive in this sense would mean S2 is likely a negative charge responding to S1's positive charge field lines, and negative would mean S2 is a positive charge repelled by S1 which also has a positive charge. If S1 and S2 are meant to represent stimuli and responses in a different context like neuroscience, behavioral science, or experimental design, the question could require a completely different answer involving stimuli-response relationships.