The steady state temperature profile of a rectangular sheet of metal inside a furnace can be obtained by solving the following partial differential equation;
$$\frac{{{\delta ^2}T}}{{\delta {x^2}}} + \frac{{{\delta ^2}T}}{{\delta {y^2}}} = 0$$
The number of boundary conditions needed to solve this equation are:

A. one in x-direction, one in y-direction

B. two in x-direction, two in y-direction

C. two in any of the two directions

D. four in any of the two directions

Answer: Option B