J, L, M, N, O and P are members of a spy network for security reasons, only certain spies are able to contact other spies. The only contacts allowed are:
J can contact both L and N.
O can be contacted by L, M and P.
N can contact M.
O can contact both L and N.
P can be contacted by M.
A spy can receive a message from any spy who can contact him and , in relay the message to any spy he is able to contact.
If, for security reasons, O cannot be contacted, which of the following message can be sent, either directly or with an intermediary?

Options

A. J to P
B. L to M
C. J to M
D. M to L

Answer

A

Explanation

Begin with the first condition.
J can contact both L and N:

Next, O can be contacted by L, M and P :

Next, N can contact M :

Then, O can contact both L and N :

Finally, P can be contacted by M:

With a "network" set, any further conclusions that you might need to draw are already implicit in the diagram. For Example, J can have N relay a message to M, who in turn can relay the message to O :

So there is no need to look for further conclusions. Go to the questions.
The modified diagram looks like this :
On the actual test, you would block out O in your mind.s eye. Our modified diagram shows that J is still able to get a message to P :

The diagram shows that none of the other communication is possible.