Which are tangents 
We are asked to see which are tangents and which aren't. I think B3, bottom left and bottom middle are not tangents
 A: A tangent to a curve is a straight line that just touches the curve, such that the slope of the tangent is exactly that as the slope of the curve. By that definition, all except for B5 display tangents.
EDIT: The picture is unclear, so it is difficult for me to tell in the cases of B3 and B4. A larger picture would help, or you could judge this yourself using the definition I provided above.
A: B1 and B2 are clearly expressing the unique tangent lines at $x=0$ in your image. 
There are infinitely many lines "touching" at $x=0$ on B5, but no unique defined tangent line. 
B6 is clearly expressing the unique tangent line at $x=0$. 
There are definitely no tangent lines being expressed in B3. 
In B4 one is definitely not the tangent line, but the other does appear to be the tangent line at $x=0$ (I cannot see the names of the two lines but I think it says $c_2$).
We define the tangent line to a curve $f(x)$ at a point $P(x_0,f(x_0))$ as being the unique line through $P$ with slope 
$$\lim_{h \rightarrow 0} \frac{f(x_0+h)-f(x_0)}{h}.$$
If this slope does not exist, then there is no tangent line at $P$.
