[填空题]在三棱锥P—ABC中，∠ABC=90°，∠BAC=30°，BC=5，又PA=PB=PC=AC，则点P到平面ABC的距离是______．

[多项选择]当8255 PA口工作于方式2，PB口工作于方式0时，其PC口可用作( )
A. 全部联络线
B. 部分联络线
C. 部分I/O
D. 一个8位I/O
E. 两个4位1/O

[填空题]下面是8031扩展8255A初始化程序，其PA口设置成______，PB口和PC口设置成______。 MOV A，#90H MOV DPTR，#7FFFH MOVX @DPTR，A MOV DPTR，#7FFCH MOVX A，@DPTR MOV DPTR，#TFFDH MOVX @DPTR，A

[单项选择]如图6-82，△ABC中，∠BAC=90°，以AB为直径的圆交BC于D，则图中阴影部分的面积为（）。
(1)AB=2； (2)AC=2．
[*]
A. 条件(1)充分，但条件(2)不充分．
B. 条件(2)充分，但条件(1)不充分．
C. 条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分．
D. 条件(1)充分，条件(2)也充分．
E. 条件(1)和(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．

[简答题]若程序P_a和P_b单独执行时分别用T_a和T_b，T_a=1小时，T_b=1.5小时，其中处理器工作时间分别t_a=18分钟，t_b=27分钟，如果采用多道程序设计方法，让P_a、P_b并行工作，假定处理器利用率达到50%，另加15分钟系统开销，请问系统效率能提高多少

[单项选择]已知事件A和B的PAB=0.4，PA=0.8，则PB|A=（）
A. 0.5
B. 0.6
C. 0.65
D. 0.7

[单项选择]过正方体一侧面的两条对角线交点，与下底面四个顶点连得一四棱锥，则四棱锥与正方体的体积比是多少？（）
A. 1∶8
B. 1∶6
C. 1∶4
D. 1∶3

[简答题]

菱形ABCD在平面α上，PA⊥α，求证：PC⊥BD。

[名词解释]pA₂

[单项选择]PB America Trust Company
1345 Bay Street
Seattle, WA 64592
December 10, 2009
Mr. James Berkeley
Human Resource Division
Wetherby Insurance Brokers Inc.
656 Hyde Street
Tampa Bay, FA 92564
Dear Mr. Berkeley:
I am writing on behalf of Mr. Kenneth Wyatt, who is interested in applying for an insurance broker position with your company. For the past three years Mr. Wyatt has been a valued employee at America Trust as part of the co-op program of the School of Business at the University of Seattle, Washington. During this time, I oversaw Mr. Wyatt’ s work. From day one, Mr. Wyatt established himself through his dedication and his ability to learn quickly and work independently. In fact, we were so impressed with his capability that we were interested in offering him full-time employment. However, he wishes to live and work in Tampa Bay in order to be closer to his f
A. Before entering the School of Business
B. After working for Wetherby Insurance Brokers Inc.
C. Shortly after graduation from university
D. During his studies as a university student

[填空题]安装了Windows98的PC机可以在三种不同的网络中起不同的作用，它们分别是远程网络、客户/服务器网络和对等式网络。如果某局域网中，所有的主机(计算机)均使用Windows98操作系统，则该网络属于 ______。