PubNub publishes and subscribes . . . . . . . . in order to send and receive messages.

The correct answer is: channels.

PubNub is a real-time data streaming platform that allows you to publish and subscribe to channels in order to send and receive messages. A channel is a logical grouping of messages that are related to a specific topic. When you publish a message to a channel, all subscribers to that channel will receive the message. When you subscribe to a channel, you will receive all messages that are published to that channel.

The other options are incorrect because:

• A network is a group of computers that are connected together. PubNub does not require you to be on a specific network in order to use it.
• An account is a way of identifying yourself to PubNub. You need to have an account in order to use PubNub.
• A portal is a web-based interface that allows you to manage your PubNub account. You do not need to use the portal in order to publish and subscribe to channels.
• Keys are used to authenticate your PubNub account. You need to have keys in order to publish and subscribe to channels.

I hope this helps! Let me know if you have any other questions.