The following passage is the draft of an excerpt from a contemporary book about maintaining health.

(1) Curiously, there is good evidence that for many people, an increase in body weight might not require an increase in calorie consumption at all.
(2) In most scientific studies it is difficult to determine how much people are eating, because appetite regulation is a field of staggering complexity.
(3) (Have you ever had to tell your doctor whether you drink beer or binge out on chips or ice cream?)
(4) But in certain controlled environments, where sneaking in an unreported chocolate bar is unlikely, interesting insights can be gained.
(5) U.S. prisons have long been fertile ground for nutrition research, with a number of prisoner-feeding experiments being conducted over the years.
(6) Overfeeding studies in the twentieth century by the researcher Erich Sims showed that subjects gain different amounts of weight despite eating identical amounts of food, indicating that the “calories-expended” side of the equation varies considerably between individuals, independent of exercise or other physical activity.
(7) It also showed different amounts of resistance to weight gain, as subjects’ metabolic rates seemed to increase on overeating, their bodies trying hard not to lay down too much of their excessive food intake as fat.
(8) The extent to which this happened varied significantly among individuals, despite the similarity of their diet and environment.
(9) These results are only curious if we assume that everyone reacts to food in exactly the same way.
(10) Experience tells us, however, that it is a bit more complicated than that.
(11) Everybody processes their food differently.
(12) You might burn calories faster.
(13) Another person stores more calories.
(14) What is eaten also matters since reaction varies based on nutritional intake.
(15) That applies even when people appear in terms of their age, height, and weight dimensions are equivalent.
(16) A diverse population would have a number of evolutionary advantages, with some individuals prioritizing the effective storage of fat in order to survive and others burning most of their energy exploring.
(17) It would also make sense for us to be able to switch between those two states when we needed to.
(18) But how is it that the amount of weight gained from identical food intake can vary among individuals?
(19) Even though hormones regulate our feeding, we only store calories when we eat more than we burn, right?
(20) When we consider the “calories out” side of the equation, we almost always look at exercise as the most important factor, largely because it is the one area that we can easily change.
(21) But basal metabolism is by far the largest chunk of the energy we burn.
(22) We generally expend around half our calories staying alive, and another 10 percent staying at the right temperature.
(23) Around 30 percent goes towards physical activity, and the remaining 10 percent on digesting food.

In sentence 2 (reproduced below), which of the following versions of the bolded text best explains the writer’s position expressed in the main clause of the sentence?

In most scientific studies it is difficult to determine how much people are eating, because appetite regulation is a field of staggering complexity.
A) (as it is now)
B) researchers seldom ask the right questions
C) different foods have varying impacts on the digestive system
D) people generally submit their own data and this isn’t seen as reliable
E) psychological factors determine why certain foods are more popular than others

(source: AP English Language online test 2 from Barrons)