Answer the following true or false:

a) Every surface has exactly two different possible orientations, corresponding to the different signs of the normal vectors.

b) The curl of the vector field F = <0,x,0> is zero.

c) The gradient vector points in the direction of the maximum rate of change.

d) If the limit lim(x,y)->(a,b) f(x,y)=L, then the value of f(x,y) must approach L along any path to (a,b).