Final answer:
The term 'grok' from Heinlein's novel refers to a deep, empathetic form of understanding and communication. Option a is correct.
Step-by-step explanation:
The word from Heinlein's "Stranger In A Strange Land" that means "to communicate sympathetically" is grok.
This term encompasses a profound understanding so thorough that the observer becomes a part of the observed.
To grok something is to assimilate it so completely that it is part of oneself.
Therefore, option a is correct.