کدام جمله زیر معنای "تا زمانی که او برگردد، من کتابم را تمام خواهم کرد" را می‌رساند؟

a) By the time he comes back, I will finish my book

b) By the time he comes back, I will have finished my book

c) When he comes back, I will finish my book

d) When he comes back, I have finished my book