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

Question

Once the frost has ____ the bulbs can be lifted and stored for the winter.

Accepted Answer

A. passed,. An introductory dependent clause is followed by a comma.

Answer

B. passed — No comma runs the clause into the main clause.

Answer

C. passed; — A semicolon can't follow a dependent clause.

Answer

D. passed, then — 'Once … then' is not needed; the comma alone suffices.

Standard English Conventions practice question