Black holes were once considered purely theoretical ______ today, astronomers have observed dozens of them across the universe.
Which choice completes the text so that it conforms to the conventions of Standard English?
- A
, though,
- Bcheck_circle
;
- C
(empty)
- D
,
Explanation
A semicolon joins two related independent clauses cleanly. ", " is a splice; " " is a run-on; ", though," is over-punctuated.