透镜有两类：中间厚边缘薄的透镜叫______，它对光有______作用，中间薄边

—What do you use computers to do?        

—They are useful.  For example, they can      _ sending e-mail.           [ ]

A. use to

B. be used of

C. be used for

若a>0，b<-2则点(a，b+2)在[ ]

A.第一象限

B.第二象限

C.第三象限

D.第四象限

下列除哪项外，均属于虚性闭经的病因病机：

A．肝肾不足

B．痰湿阻滞

C．气血虚弱

D．阴虚血燥

E．脾虚血少

局部黏膜抗感染的主要免疫球蛋白是（）

A.IgG

B.IgM

C.SIgA

D.IgE

E.IgD

Compared with this year, the estimated world oil growth for 2005 will ______. a. be 84 million more barrels per day b. increase by 2.5% c. be up 2.53 million barrels per day d. be up 1.8 million barrels per day