Of the following, which knot can be tied in the middle of the line?

The running bowline is designed to create a secure loop at the end of the line, which can also be tied in the middle of a rope. This flexibility allows it to be used in various applications where a loop is needed without needing access to the ends of the rope. The running bowline maintains its strength while ensuring that the knot can be adjusted or slipped if necessary.

The other knots mentioned have different characteristics and limitations. For instance, the timber hitch is primarily used for securing a line to a cylindrical object and is not suitable for tying in the middle of the line. The sheep shank is effective for shortening a length of rope or adding a hitch, but it is not tied in the middle for creating a loop. The figure eight is primarily used to prevent the rope from slipping and is generally tied at the ends, making it unsuitable for being tied mid-line. Thus, the running bowline stands out as the appropriate choice for this scenario.