Write
1897/ Jack London/ 21/ year/ old/ gold/ discover/ Alaska
A.In 1897, when Jack was 21, gold was discovered in Alska.
B.On 1897, when Jack was 21, gold was discovered in Alska.
C.In 1897, when Jack had been 21, gold was discovered in Alska.
D.In 1897, when Jack was 21, gold had been discovered in Alska.