The number of plant and animal species that humans are known

[Luci]

Can anyone explain this structure. I think this is a tough one for a nonative. I didnt like any of the options. Is there a rule for such kynd os sentences? For example, it seems that they must use the "to" plus present perfect (to have forced)
Any help will be great

Thanks

[praanav]

Since the action started in the past and is ongoing you need to use present perfect tense.
A - only choice that use the present perfect tense
B - tense error
C - Tense error
D - Awkward
E - passive voice

Can anyone explain this structure. I think this is a tough one for a nonative. I didnt like any of the options. Is there a rule for such kynd os sentences? For example, it seems that they must use the "to" plus present perfect (to have forced)
Any help will be great

Thanks

[dbernst]

praanav, thanks for the assistance!
-dan

[S.agar]

@Dan..Could you please guide me why option E is wrong. I agree that E is written in passive mode however the sentence also uses Present perfect tense similar to Option A. Please Correct me if I am wrong.

[RonPurewal]

@Dan..Could you please guide me why option E is wrong. I agree that E is written in passive mode however the sentence also uses Present perfect tense similar to Option A. Please Correct me if I am wrong.

"Known as" precedes the name of something.

E.g.,
The total disappearance of a species is known as extinction.

Choice E does not give the same of something, so it's nonsense.

[RonPurewal]

By the way, this sentence could also be written correctly as "...known to have been forced to extinction by humans..."

There's no objective reason to write it in the active form (with "humans" as subject); the purpose there is purely to emphasize the role of humans (such evil creatures!) in these extinctions.
(You'll never be asked to choose between two correct versions of a sentence, so you'd never have to choose between the OA and this version. Just make sure you understand how both of them work—and that both of them work.)

[S.agar]

Thanks you Ron for always be so helpful :)

[jlucero]

Glad that it helped.