Achmed Has Invented a Mechanism for Building Barbwire Fences

Achmed has invented a mechanism for building barbwire fences. It consists of a motorized machine that stretches the barbwire between two fence posts. It then wraps the barbwire around the post, ensuring that the fence is stable. The beauty of the mechanism is that at no point must a person touch the wire, thus drastically reducing the fear of injury. However, there are still a few glitches in the system. For example, the machine stretches the wire too much, causing the wire to snap before the fence is complete, and flail about until the operator turns off the machine. This increases the potential safety hazard, as the broken barbwire swings about dangerously until the machine is turned off. Additionally, if the operator does not turn it off in time, the loose barbwire ends up damaging the machine. Achmed is convinced that with a bit of tinkering, he can get it working better. Which of the following is TRUE of Achmed's invention?

A) It is not patentable but may be protected as a trade secret.
B) It is not patentable, but may qualify as an industrial design.
C) It is patentable, so long as Achmed has not told others of its existence.
D) It is patentable, so long as it has not already been patented by someone else.
E) It is patentable, so long as within sixty days of filing the patent application, the design is fixed to avoid all the glitches.