The passage given below is followed by four alternate summaries. Choose the option that best captures the essence of the passage.

A distinguishing feature of language is our ability to refer to absent things, known as displaced reference. A speaker can bring distant referents to mind in the absence of any obvious stimuli. Thoughts, not limited to the here and now, can pop into our heads for unfathomable reasons. This ability to think about distant things necessarily precedes the ability to talk about them. Thought precedes meaningful referential communication. A prerequisite for the emergence of human-like meaningful symbols is that the mental categories they relate to can be invoked even in the absence of immediate stimuli.

The paragraph says that humans think about past occurrences suddenly without any immediate stimuli.
The author also says that thinking/thoughts about a certain distant past is a necessity before one can speak about it. 
He says that thoughts are a pre-requisite before one talks about it. He also gives an example that various human-like symbols might have emerged without any immediate stimuli.

Option A and C: There is no mention of specificity to humans in the passage
Option B : "All speech acts" is a false generalisation. The passage says that speaking about distant past requires thinking about it first
Option D : It clearly captures the essence of the passage and says that one needs to think about distant past events before talking about them
Hence option D is correct.