Because nourriture is feminine so you would have to add the extra "e" in parfait
Parfait/parfaite does not mean completed but perfect.
Or have I misunderstood you?
please someone tell me how do you know masculine from feminine I need help!this is causing many mistakes for me
Unfortunately you have to remember them by heart, which is painful and one of the hardships of learning French. Now it could be worse: German has three genders :)