The volcano had been dormant for over 500 years ______ then, in 1980, Mount St. Helens erupted with devastating force.
Which choice completes the text so that it conforms to the conventions of Standard English?
- A
,
- B
(empty)
- Ccheck_circle
;
- D
, but
Explanation
A semicolon properly joins two related independent clauses. ", " is a splice; " " is a run-on; ", but" introduces an explicit contrast that isn't necessary.