What do you mean? Mie îmi plăcea de tine would be the past: I liked you.
But in the exercise there is no English to compare to so you have past and present to choose from which both make sense.
Probably you met a silghly different version than mine, but no. Present and past simple (plăcea) are not interchangeable here.
I assume it was a multiple choice exercise, and that too should have been two.