I think its B but I want someone else to chime in because C isn't necessarily incorrect.

A is wrong because the dependent clause should be in the future perfect tense

B correct

C I think its grammatically correct as well, so I hope someone else can chime in

D Shall changes the meaning

E Since we have yet to reach peace and happiness the use of the conditional tense is wrong.

IMO A

first lives will be wasted then peace will come.
here we need to use future perfect tense.
it is like
By the time peace and happiness come to the planet, many lives will have been wasted

but do we get such kind of SCs in GMAT?

What is the source plz

Also OA plz

I think it is B, but just by instinct !! OA will probably explain.

One more for B

Trying a new method to explain ( inspired by the method on some website on which I learnt tenses)


(many lives wasted).........................(peace comes to the planet)
____ |_____________________________|_________________________ (time-line)



To show the precedence of one event, we use the perfect tense. With the case in hand, our objective is to show that before peace comes to the planet, many lives will be wasted. Hence, we will have to use future perfect tense together with adverbial clause "By the time"

As 'will have been' is appropriate, eliminate options A and D. Eliminate E as it has a hint of uncertainty 'would' and the author is almost certain.

Now the tougher part. 'By the time' itself refers a point in future and we use simple present form of verb to show the future occurrence. For e.g "By the time I complete this explanation, I will have spent at least 20 minutes of my office hours"

Hence, 'come' together with 'by the time' is sufficient to show a future event.

Considering all this, B satisfies every condition and can be termed as "The One"

OA is B.