What does the semicolon in the following phrase do? he had not thought of that; he stammered: a. introduces the driving action b. links independent clauses c. connects two pieces of dialogue d. introduces a quotation

The semicolon in the above phrase is used as it:  

B. Links independent clauses

Explanation:

A semi-colon helps in joining two independent and closely related clauses.  The independent clauses need not be joined by any coordinating conjunction. In the above sentence, the semi-colon is joining the two independent clauses.

tending to cause harm

the purpose of the heading in the passage is to identify who is telling the story.

this excerpt is part of the book sugar changed the world (2010) written by marc aronson and marina budhos. as the book has been written by two people, the heading "marc" indicates that this specific excerpt is being narrated by aronson. in the fragment, marc describes his grandfather's story after hearing it from his cousin. however, there are other excerpts where budhos is the one that tells the story of her family.

aronson and budhos, who are husband and wife in real life, decided to write sugar changed the world when they found out how sugar, which had an important role in slavery and economy, changed their ancestors' lives.