Read the Paragraph Below and Answer the Questions That Follow

Read the paragraph below and answer the questions that follow.
(1) Horace Bristol might be the only photographer to owe his fame to his child's book report. (2) Before he became an architect, Bristol had been a documentary journalist. (3) One day his teenage son was writing a report on The Grapes of Wrath , John Steinbeck's novel about an Oklahoma farm family forced off their drought-stricken land during the 1930s. (4) He asked his father if he'd ever read the book. (5) Not only had he read it, Bristol replied, he had dreamed up the idea for it, recruited Steinbeck to write it, and photographed thousands of real farm families forced to leave their homes. (6) After revealing his past to his son, Bristol the photographer came out of hiding. (7) Hoping to sell a few of his photographs, he was soon astounded by the prices they commanded. (8) Encouraged, he took up his camera once again. (9) Since then, the photographs of Horace Bristol have become famous. (10) His images of despair during the Depression, heroism in the Pacific during World War II, and postwar poverty and hope in rural Korea are among the greatest photographs of the twentieth century.
In the paragraph above, transitional expressions that indicate time include all of the following except :

A) before
B) one day
C) since then
D) not only