Mark delayed writing the book until he had done a...

Câu hỏi: Mark delayed writing the book until he had done a lot of research.

A Mark did a lot of research after he finished writing the book.

B It was only when Mark had written the book that he did a lot of research.

C Mark delayed writing the book as he had already done any research.

D Only after Mark had done a lot of research did he begin to write the book.