以蚕豆叶为材料观察气孔时，最好撕取蚕豆叶的（ ） A．上表皮 B．下表皮 C．叶

现存人类最早的文字是哪里、谁发明的、什么文字？

某建筑场地采用预压排水固结法加固软土地基。软土厚度10m，软土层面以上和层底以下都是砂层，未设置排水竖井。为简化计算。假定预压是一次瞬时施加的。已知该软土层孔隙比为1.60，压缩系数为0.8MPa^-1，竖向渗透系数K_v=5.8×10⁷cm/s，其预压时间要达到下列（）d时，软土地基固结度就可达到0.80。

A．78

B．87

C．98

D．105

—John, what was your sister doing while you _____ the piano?

—Oh, she _____ with toys.[ ]

A. played; played

B. played; was playing

C. were playing; played

D. were playing; was playing

属于纤溶酶原激活物的是（）

A.t-PA

B.u-PA

C.UK

D.PA

E.Ⅻa

土质均匀且地下水位( )基坑(槽)或管沟底面标高时，其挖方边坡可做成直立壁不加支撑。

A．高于

B．低于

C．等于

D．2倍于