Question $8\mathrm{.}13-$ A steel bar is placed on top of an identical bar and then

welded together, as shown in Fig. $8\mathrm{.}08.$

Fig. $8\mathrm{.}08$

The ratio of their bending stiffness after welding to the stiffness before

welding is:

A$.2$

B$.4$

C$.8$

D$.16$