What is attached to the top of the tabling and snaps into the tail line of the preceding flag?

The correct answer is a ring, which serves a critical role in the process of flag signaling and display. In maritime practices, especially when securing flags, a ring is typically used to connect the tabling at the top of a flag to the tail line of the previous flag. This creates a secure and efficient way for flags to be displayed in succession without them becoming tangled or misaligned.

The use of a ring provides both stability and ease of handling during hoisting and lowering operations. It ensures that flags can move freely while also being firmly attached enough to withstand changes in wind or motion of the vessel. This is vital because flags can be subjected to varying conditions at sea, and maintaining their alignment and security is important for visibility and signaling purposes.

In contrast, other options such as a hook or a clamp may suggest different methods of attachment but do not specifically indicate the standard practice for connecting flags in this particular context. A fastener, while it could refer to any device used to secure something, lacks the specificity and traditional use associated with flag hoisting. The ring is the conventional choice for this purpose, which is why it is the correct answer in this instance.