According to Newton’s law of cooling, the heat transfer from a hot body to a cold body is

directly proportional to the surface area
directly proportional to the difference of temperatures between the two bodies
either (a) or (b)
both (a) and (b)
✅ The correct answer is option D.

The shear stress at a point in a shaft subjected to a torque is

directly proportional to the polar moment of inertia and to the distance of the point from the axis
directly proportional to the applied torque and inversely proportional to the polar moment of inertia
directly proportional to the applied torque and the polar moment of inertia
inversely proportional
✅ The correct answer is option B.