Question on-nov

3.1 Boundaries - Colon for explanation or list
0:00

On November 2, 1772, amid rising tensions with Great Britain, Boston colonists formed the Boston Committee of Correspondence. By 1774, what had started as a local means of mobilizing support for the Patriot cause had grown into something far more blank network of such committees that, facilitating communiion among the colonies, helped lay the groundwork for the Continental Congress.  

Which choice completes the text so that it conforms to the conventions of Standard English?

A.

extensive: a 

B.

extensive; a

C.

extensive, it was a  

D.

extensive. A