单项选择题 The human beings should preserve the buildings of the past to visit them for enjoyment and learn ______ life was like when they were first built． A．how B．that C．which D．what

未知题型 直径D=300mm，壁厚δ=5mm的钢管，于输水时突然瞬时关闭出口处阀门，要求产生的水击压强Δp≤1000kN/m2，求此时最大允许流量。(水弹性模量E0=2.07×105N/cm2，钢管弹性模量E=206×105N/cm2，声音在水中的传播速度为1440m/s)

未知题型 距肛门部7cm发现广基的直肠绒毛状管状腺瘤，大小约1.5cm，最合适的治疗方法为A.定期复查肠镜###SXB