In the Two$-$level Model of Multithreading Models if a thread makes a blocking system call what happen. $(3$ marks$)$ What is the benefit of using Thread Pools. $(3$ marks$)$ One of OS Services is Accounting "Explain in Arabic by your own language" $(2$ marks$)$ mention one vulnerability of the OS Simple Structure. if possible give me $3$ examples each example with $3$ processes info; and the $3$ examples have the same average waiting time based on FCFS; if not possible explain, if possible give me examples and explain. $(3$ marks$)(7$ marks$)$