Except as provided in subparagraphs (B) and (D) of this paragraph and in paragraphs (4) and (5), an employer shall pay the amount determined under
section 1391 of this title, adjusted if appropriate first under
section 1389 of this title and then under
section 1386 of this title over the period of years necessary to amortize the amount in level annual payments determined under subparagraph (C), calculated as if the first payment were made on the first day of the plan year following the plan year in which the withdrawal occurs and as if each subsequent payment were made on the first day of each subsequent plan year. Actual payment shall commence in accordance with paragraph (2).