Unemployment in USA is        to remain high in 2010, and possibly for the next few years.

A．likely

B．necessary

C．gradual

D．normal

如图3-23所示的桁架上弦杆O₁的内力为：（）

A.1.5P(压力)

B.1.5P(拉力)

C.(压力)

D.(拉力)