Option C is the correct answer.

In English, the preposition "to" is used with "known" when indicating that someone is recognized or familiar to a person or group. The correct construction is "is known to us," meaning Mr. Jackson is familiar or recognized by us.

Option A: 'By' is used with "known" in passive constructions to indicate the agent (e.g., "He is known by his friends for his kindness"). However, here, "us" is not the agent performing the knowing but the group to whom Mr. Jackson is familiar, so "by" is incorrect.

Option B: 'With' cannot beused with "known" in this context. "With" might indicate association or accompaniment (e.g., "He is popular with students"), but it doesn’t fit the structure of "is known" for familiarity.

Option D: 'On' cannot be used with "known" in this context. "On" is typically used for topics or reliance (e.g., "known on the topic"), not for indicating familiarity to a group.