Which of the following commands displays the number of system calls per second that are being executed？（）

单项选择题Whichofthefollowingcommandsshouldbeusedtoshowhowmuchdataisreadfromorwrittentoaparticularlogicalvolume，giventhereareseveralotherlogicalvolumesonthesamedisk？（）

A. sar
B. lslv
C. iostat
D. filemon

单项选择题WhichofthefollowingcommandsshouldbeusedtomonitordiskutilizationduringthetimeasystemisexperiencingadiskI Operformanceproblem？（）

A. istat
B. topas
C. vmstat
D. filemon

单项选择题Afterrunningthevmstatcommand，whichofthefollowingwouldmostlikelycausethevalueintheblockedcolumntobeunusuallyhigh？（）

A. Kernel thread
B. Too many users
C. Memory shortage
D. Network contention

单项选择题Whichofthefollowingcommandsismostusefulininitiallycollectingdatatodetermineanetworkperformanceproblem？（）

A. ping
B. trace
C. ifconfig
D. lsattr

单项选择题To examine the Exhibit， press the Exhibit button. While a user is compiling a C program，  vmstat 120 10  is run to determine the cause of a performance problem.  Given the vmstat output as shown in the exhibit， which of the following conclusions should be drawn about the I O bottleneck？（）

A. There is a file I/O bottleneck.
B. There are too many open files.
C. There appears to be a buffer shortage.
D. There is a paging space I/O bottleneck.