The truss shown is loaded at joint (B) with a vertical load of (90 mathrm {kN} \). Both members of the truss have a cross-sectional area of (4 \mathrm{-cm}^{2} \) and a length of\(1\mathrm {-m} \), and both are made of steel. The vertical displacement of joint (B) is most nearly: (A) (1.0 \mathrm{-mm}\) (B) (2.1 \mathrm{-mm} \) (C) (3.3 mathrm{-mm} \) (D) (8.6 \mathrm{-mm} \)