【单选题】338 / 952线弹性拉压杆应变能公式为?AFN2l/(2EA)F_N^2l/(2EA)FN2l/(2EA)正确BFNl/EAF_Nl/EAFNl/EAC2FN2l/EA2F_N^2l/EA2FN2l/EADFN/AF_N/AFN/A参考答案A参考解析FN2l/(2EA)F_N^2l/(2EA)FN2l/(2EA)。