In an Activity-on-Arrow network, which of the following rules of network logic are mandatory?1. Any two events can be directly connected by not more than one activity.2. Event numbers should not be duplicated in a network.3. Before an activity may begin, all the activities preceding it must be completed.Select the correct answer using the code given below.

• A. 1 and 2 only
• B. 2 and 3 only
• C. 1 and 3 only
• D. 1, 2 and 3