By the time he was twelve, Edison _______ to make a living by himself.

1. A.
   would begin
2. B.
   has begun
3. C.
   had begun
4. D.
   began

By the time he was twelve, Edison ________ to make a living by himself .

  A. would begin     B. has begun    C. had begun    D. was begun

By the time he was twelve, Edison ________ to make a living by himself .

A. would begin     B. has begun    C. had begun    D. was begun

By the time he was twelve, Edison _______ to make a living by himself.

By the time he was twelve, Edison _______ to make a living by himself.