Explanation:

- The phrase "Actual possession of property by another must put of such property on his guard" suggests that when someone else is in possession of a property, it alerts certain parties to investigate or inquire into the nature of the possession.

- Purchaser: ?? Correct Answer. When a purchaser notices someone else in actual possession of a property, the purchaser should be cautious and investigate further to understand the nature and legality of that possession. This serves as notice or a warning that there might be more to the property's legal status than meets the eye.

- Municipality: They handle local governance and infrastructure but aren't directly involved in property transactions. Actual possession doesn't necessarily alert them for property purchase concerns.

- Seller: They should be aware of the possession situation but are primarily concerned with transferring property, which might already be known to them.

- Registration office: This office is involved in the legal documentation of property transactions but isn't directly involved with possession concerns unless brought to their attention.