What can be a command that causes the following protection state transition?
a) create object o2; enter w into a[s1, o1]; delete x from a[s1, o2]; enter r into a[s2, o2]
b) create object o2; enter r into a[s1, o1]; delete x from a[s1, o2]; enter w into a[s2, o2]
c) create object o2; delete x from a[s1, o1]; enter w into a[s1, o2]; enter r into a[s2, o2]
d) create object o2; enter w into a[s1, o2]; delete x from a[s1, o1]; enter r into a[s2, o2]
