I ( ) the book but I ( ) not sure when I ( ) it...下列选项哪个正确，为

I ( ) the book but I ( ) not sure when I ( ) it...下列选项哪个正确，为什么？
I ( ) the book but I ( ) not sure when I ( ) it.
A have read ... am ... have finished B have been reading ... am ... will finish
C read ... was ... would finish D will ... am ... will have finished
为什么不选C