D

To determine whether E1 and E2 represent constant electric fields, we analyze the expressions for E1 and E2 given in the question.

Step 1: Analyze E1
The expression for E1 is given as:

E1 = x + y

Here, E1 is a function of both x and y. For E1 to represent a constant electric field, it must not vary with position (x, y). Since both x and y are independent variables, E1 is not constant, and thus it cannot represent a constant electric field.

Step 2: Analyze E2
The expression for E2 is given as:

E2 = xy^2 + x^2 y

Here as well, E2 depends on both variables x and y. Similar to E1, since E2 also varies with position, it cannot be constant either.

Conclusion:
Since both E1 and E2 do not represent constant electric fields, the correct answer is D: none of these.