For years you have had a pet box turtle named Bob that roamed freely in your yard. And for years, Bob has gone into hibernation every October. Curious about the environmental cues that govern this behavior, you decide to keep Bob in the spare bedroom with the windows sealed agains light, the temperature kept constant, and the lights on all day every day. Bob gets plenty of food and seems happy enough. He moves around and grows during the summer, and the first year of your experiment, he goes into hibernation in October. But the second year, he's a bit off and starts hibernating in September. The third year he starts in August, and the fourth year he starts in July. From this information what is reasonable to conclude?

Circannual rhythm is derived from the Latin words 'circa' meaning approximately and 'annual' meaning 'a period of one year.' So, Circannual rhythm can be defined as a biological rhythm in loving beings that occurs annually. This rhythm happens even in the absence of environmental cues. The rhythm was developed by Ted Pengelley and Ebo Gwinner.

In the given case, the circannual rhythm of Bob, a tortoise, is of 11 months as he hibernated in the first year in October, then in September, and then in August.

So, the correct answer is circannual rhythm of 11 months.