Assume there are two processes P1 and P2 designed as follows and they are launched on a single CPU system. Variables global variables. Time left P1 P2 L1: a++; L5: a--; L2: b++; 16: b--; L3: L7: d--; C++; L8: 14: ... ... As shown in the example codes above, L1 through L6 are labels indicating the operations on variables along the process execution. Particularly, we know those operations are not atomic. If the initial value for all the four variables is 5, P1 and P2 arrive at the system the same time. When processes P1 runs to L4, and P2 runs to L8, which is the following statement is NOT correct? a. variables a and b have determined value, which is 5 b. variable c has a determined value of 6 O c. variables a and b have undetermined values, they may be equal to 4, 5, or 6 d. variable d has a determined value of 4