ANS:A - Logarithmic mean area

In the case of heat flow by conduction through a cylinder, the appropriate area to consider is the surface area perpendicular to the direction of heat flow. This area is commonly referred to as the "mean area" or "average area." However, the type of mean used for this purpose depends on the geometry of the cylinder and the specific heat transfer problem. In general, for a cylindrical geometry, the appropriate mean area to use is the "geometric mean area." Therefore, the correct answer is: Geometric mean area.