The correct answer is: B. heartbeats
NameNode and DataNode do communicate using heartbeats. Heartbeats are a way for the NameNode to keep track of the DataNodes in the cluster. The NameNode sends out heartbeats to the DataNodes at regular intervals, and the DataNodes respond with heartbeats to acknowledge that they are alive. If the NameNode does not receive a heartbeat from a DataNode for a certain period of time, it will assume that the DataNode is dead and will remove it from the cluster.
Active pulse is a term used in electronics to describe a signal that is constantly on. This is in contrast to a passive pulse, which is a signal that is only on for a short period of time. H-signal is a term used in telecommunications to describe a signal that is used to carry data. Data pulse is a term used in computer science to describe a signal that is used to carry data.
In conclusion, the correct answer is: B. heartbeats.