与国内债券相比，国际债券具有（）等特点。 A.存在信用风险 B.存在汇率风险 C.发

如图所示，镜前竖直插两根大头针a和b，观察a和b的像重叠在一起的情形，其眼睛应放在（　　）

A．通过a、b的直线上

B．通过a、b像的直线上

C．通过a垂直于镜面的直线上

D．通过b垂直于镜面的直线上

A company does research about cash flow statements and gathers the following transactions in 2011:

Purchased securities held for trading	$3000
Purchased property, plant, and equipment	$4500
Proceeds from sale of plant	$3500
Losses on sale of plant	$1500

Based on this information, the net cash flow from investing activity in 2011 is closest to:

A. -$4000
B. -$2500
C. -$1000

煤矿行业对采区回采率有明确的规定：中厚煤层回采率不低于（）%。

A、75

B、80

C、85

D、90

油罐四周应设立环形地网，接地电阻应小于（）Ω。

A.4

B.10

C.4K

D.10K

请简单说一说如何选择网络信息资源？主要的标准有哪些？