Reminder: A (1,2,2), B (2,-1,0), C (4,5,-1) and D (5,2,-3)
Midpoint E of the rectangle:
$$\mathbf{e} = \mathbf{a} + \frac{1}{2}\overrightarrow{AD}$$
$$= \mathbf{a} + \frac{1}{2}(\mathbf{d} - \mathbf{a})$$
$$= \frac{1}{2}(\mathbf{a} + \mathbf{d})$$
$$= \frac{1}{2}\left[(1,2,2) + (5,2,-3)\right]$$
$$= \frac{1}{2}(1+5, 2+2, 2-3)$$
$$= \frac{1}{2}(6, 4, -1)$$
$$= (3, 2, -1/2)$$
So, the answer is E (3, 2, -1/2)
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