Question $3$: For a doubly reinforced beam, when the compressive strain of concrete at the top $($compressive side$)$ reaches $0\mathrm{.}003$ and the tensile strain in the rebar subjected to tension reach $0\mathrm{.}0012,$ what is the failure mode of beam $($brittle failure mode, undesirable ductile mode, or desirable ductile mode $)?(5$ points$)$