Answer:
which is Choice B
This is the same as writing 
The second "2" is not under or inside the square root.
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Explanation:
Refer to the unit circle below. I've highlighted the angle 45 degrees and its corresponding sine value. It's the y coordinate of the point on the unit circle, for this particular angle.
Therefore, 
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You could alternatively draw out a 45-45-90 triangle. Let x be the leg length and the hypotenuse is 1 unit long. Solve
for x and you should get
as the length of each leg.
Then take the ratio of the opposite over hypotenuse to find the same answer mentioned above.
Usually one will differentiate the function to find the minimum/maximum point, but in this case differentiating yields:

which contains multiple solution if one tries to solve for x when the differentiated form is 0.
I would, though, venture a guess that the minimum value would be (approaching) 5, since the function would be undefined in the vicinity.
If, however, the function is

Then differentiating and equating to 0 yields:

which gives:

or

We reject x=5 as it is when it ix the maximum and thus,

, for