关于滑轮和滑轮组的说法中，正确的有（）。 定滑轮既可以省力也可以改变用力方向。 滑轮属于杠杆类简单机械。 手拉葫芦也是一种滑轮组。 动滑轮实质是个等臂杠杆。 定滑轮实质是个动力臂为阻力臂二倍的杠杆。
A user needs to create a trigger that will update table T2 whenever a row is added to table T1. Assuming the user has all appropriate privileges for table T2, which privilege is required on table T1 to create the trigger?（） REFERENCES。 SELECT。 UPDATE。 ALTER。
沼渣养殖蚯蚓，一般只要掌握“（）、（）、（）、（）、（）和（）”技术，基本就能成功。
An administrator analyzes a poorly performing system and suspects that the issue is related to CPU resource. Upon reviewing output of vmstat, the administrator is concerned with the values in the ‘pc’ and ‘ec’ columns. Which definition describes these two headings?（） 'pc' refers to the number of physical processors consumed, while 'ec' refers to the percentage of entitled capacity consumed.。 'pc' refers to the 'physical CPUs' and lists how many are left un-allocated, while ec' refers to the 'entitled CPUs' and lists what amount is currently allocated to the LPAR.。 'pc' refers to the 'processor count' and reflects how many CPUs are allocated to the LPAR, while 'ec ' refers to the 'extra capacity' and lists how much above the LPAR entitlement is being consumed.。 'pc' refers to 'processor cards' and reflects how many MCM modules are actually being used by this LPAR, while 'ec' refers to the 'entitled CPUs'and lists what amount is currently allocated to the LPAR.。
试述美国次贷危机的原因、影响与启示。
长期缺乏维生素B12可引起（）。
