Step 1: Recall properties of a rectangle
A rectangle is a quadrilateral with:
- Opposite sides equal and parallel
- All interior angles equal
Step 2: Use angle sum property of quadrilateral
Sum of all interior angles of a quadrilateral = 360\degree
In a rectangle, all 4 angles are equal. So:
\[
\text{Each angle} = \frac{360\degree}{4} = 90\degree
\]
Step 3: Evaluate options
(A) 60\degree $\Rightarrow$ Incorrect
(B) 30\degree $\Rightarrow$ Too small for rectangle
(C) 45\degree $\Rightarrow$ Diagonal halves form these, not corners
(D) 90\degree $\Rightarrow$ Correct
\[
\boxed{\text{Correct Answer: (D) 90\degree}}
\]