According to the passage, which of the following posed the biggest obstacle to the development of military forts

A．Controlling one's calorie intake is more important than doing exercise.
B．Even occasional exercise can help reduce weight.
C．Weight reduction is impossible without exercise.
D．One could lose ten pounds in a year's time if there's no in crease in food intake.

A．they think it is physically exhausting
B．they find it hard to exercise while on a diet
C．they don't think it possible to walk 3 miles every day
D．they find consulting caloric-expenditure charts troublesome