【单选题】

"Even exercise professionals concede half a point here" (Line 3, Para. 2) means "They ______."
A．agree that the calories in a small piece of pastry can be difficult to work off by exercise

B．partially believe diet plays a supporting role in weight reduction
C．are not fully convinced that dieting can help maintain one's new weight
D．are not sufficiently informed of the positive role of exercise in losing weight