Based on the drawing given on item number 1, we can easily find the line segment representing tangent theta. Line segments are found in and out of the unit circle. Unit circle has a radius 1.
Tangent theta is equal to opposite side divided by adjacent side.
So, tangent (theta) = DB / OB. Since OB is a radius, so it has the value 1.
The final equation will be tangent(theta) = DB / 1 or tangent (theta) = DB. It's choice letter B.