Each of the following functions has a maximal domain on which it is continuous and that domain has a boundary. Match the verbal description of this boundary with the function by putting the letter corresponding to the function.1. f(x, y,z)=1x2+y2+z22. f(x, y)=xln(y)3. f(x, y)=14−x2−y24. f(x, y,z)=xyzx2+y2−z5. f(x, y,z)=z1−x2−y2A. one pointB. a straight lineC. a circular paraboloidD. a circleE. a circular cylinder