Using avoir in future anterior

Question

Why is this incorrect?

They will have been experts in their field

Elles auront été .....

When I click on 'explain this' I see conjugation of avoir in future anterior. But the question said I should use être not avoir. One of the examples given has the same construction. Why cant I use avoir? I'm confused now how to form ' will have been. Advice appreciated

Thanks

Accepted Answer

Hi Sally,
'Ils auront été ...' is correct as both the verbs être and avoir take 'avoir 'as auxiliary verbs -
Elle aura été 
Nous aurons eu 
This looks like it is from a quiz, so the best way is to re-post your query using the Report It button on your correction board which will link directly to the said quiz so we can look at it.
Hope this helps!