Which of the following cohld be the legnth of the sides of a 45° - 45°-90°

I'm not exactly sure what "the following" means in your question.

Normally, it means that there's more coming, like a list of choices,

but this time it must mean something else that I don't understand.

In a right triangle with equal acute angles, the lengths of the legs

are equal, and the length of the hypotenuse is

(square root of 2) · (the length of either leg).