What is CD in the figure above?

Two ways.

First, the way I would do it: I'd look at the thing and estimate. AB is 1.7. Is CD longer or shorter? Longer. A is out. How much longer? Not much. Oh, come on, it's just barely longer. C is 2.4 and D and E are both even longer than that. CD is NOT 0.7 longer than AB. There's only one answer choice that's close.
Answer choice B.

I will never understand why, but that answer is not going to satisfy some of you, so here's the "real" math. 1 + BD^2 = 3. BD = \(\sqrt{2}\). BD = BC, so those are two legs of a 45-45-90. The hypotenuse is \(\sqrt{2}\sqrt{2} = 2\).
Answer choice B.

I can't wait to see how many people miss this one because they fall right into the trap of making BD = 2...