Every year, _______ visitors come to Taixing to enjoy the delicious food, such as Huangqiao cakes, Xuanbao dumplings and so on.

A．two hundreds

B．thousand of

C．thousands of

D．two hundred of

用平底铝锅烧水，铝锅厚1mm，导热系数为240W/（m•℃）。如果锅底上结了厚为0.1mm的水垢，水垢的导热系数为2W／（m•℃），且锅两边的温差不变，那么有水垢和无水垢的导热量之比为（）。

A.0.077

B.0.083

C.13

D.12