Four machines, A, B, C, and D are connected upon computer network. It is feared that the computer virus might have infected the network. Your security team makes the following comptuer virus statements:
1. If D is infected, then so is C.
2. if C is infected, then so is A.
3. If D is clean, then B is clean but C is infected.
4. If A is infected, then either B is infected or C is clean.
Supposing that these statements are all true, what can you conclude?