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here there are some sentences :
1.in five years'time , we......................................(find) a cure for cancer.
2. In 20 years' time , politicians .............................(ban) all nuclear weapons.
3. By the year 2010, we ..............................(find) a cure for badness.
4. By the year 2025, AIDS ...........................(kill) billions of people.
5. In the year 2020, traffic accidents ..................................(become) the third most sommon cause of death.

here are my answers,
1. will have found
2. will have banned
3. will have found
4. will have killed
5. will have become

as you see i think 3,4 are correct. but as far as i understand from grammatical knowledge
all of them are future perfect .
please help me.....
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Your answers are correct.
Also, they are all future perfect, as you say.
Any tense with the name "continuous" has an "ing" somewhere in the verb phrase. [8|]
Comments  
Students: We have free audio pronunciation exercises.
but according to book only 3,4 future perfect, the others are future continuous,
please help me,,,,
It seems your book may have a misprint.

The perfect tenses always have a form of "to have" (have, has, had, will have)
The continuous tenses always have an "-ing".

Without "-ing" it can't be continuous. "will have become", etc., are not continuous tenses.

I will have gone. = Future perfect.

I will be going. = Future continuous.

Hope that helps.