ANS:B - conduction

In the laminar sublayer of a liquid flowing through a pipe, heat transfer primarily occurs through conduction. The laminar sublayer is a thin layer of fluid adjacent to the pipe wall where the flow is characterized by smooth, orderly motion. In this region, the velocity gradients are small, and the fluid motion is predominantly in the form of fluid layers sliding past each other. As a result, heat transfer within the laminar sublayer is mainly through molecular diffusion or conduction, as the fluid molecules transfer thermal energy from higher to lower temperature regions through direct molecular collisions. So, the correct answer is: "conduction"