Answer: C. Line
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Step-by-step explanation:
Plane symmetry only applies to objects in 3D space. So choice A won't apply.
Point symmetry is where we can rotate the object some number of degrees (between 0 and 360 excluding the endpoints) and have it line up with itself. We can't do such a rotation, so this figure has no point symmetry. We rule out choice B.
Choice C works since we can reflect the upper half of the letter over the horizontal midline to have its reflection line up with the lower half, and vice versa. There is only one line of symmetry here.
Choice D is not true since choice C was shown to be true.