To determine which communication technologies employ only asynchronous communication, we first need to understand what asynchronous communication means:

• Asynchronous Communication: This is a type of communication where the exchange of information is not in real-time. Participants do not need to be present simultaneously to receive, send, or exchange information.

Let's analyze the given options:

1. Video Conferencing: This is synchronous communication because all participants must be present at the same time to interact with each other in real-time.
2. Email: This is asynchronous communication as the sender can send the message at one time, and the recipient can read and respond at a different time.
3. Forums: This is another example of asynchronous communication. Users post messages or questions at one time, and others can respond at their convenience.
4. Instant Messaging: Typically, this is synchronous communication because it often involves real-time exchange of messages, although it can be used asynchronously if messages are sent and read at different times. However, it is primarily designed for instant, real-time communication.

From the above analysis, the communication technologies that are primarily asynchronous are Email and Forums.

Therefore, the correct answer is: (c) and (b) only.