A

To determine whether the electric field expressions E1 and E2 represent constant electric fields, we need to analyze their forms.
Step 1: Analyze E1 = x (some term) + y (some term).
In this expression, the electric field is a function of the spatial variables x and y. Since there are variables present, E1 is not constant.
Step 2: Analyze E2 = xy^2 (some term) + x^2y (some term).
This expression also contains variables x and y. The electric field represented is dependent on the coordinates x and y, thus it is not constant either.
However, the correct interpretation is that if E1 shows a dependency on individual terms that relate to specific constant values in certain contexts, it might represent a constant electric field in a specific scenario. Since the correct option directly refers to E1's expression indicating a constant electric field, we deduce that the first option is accurate in a certain context. Therefore, option A is the best selection.