would have done.

As its sales of computer products have surpassed
those of measuring instruments, the company has
become increasingly willing to compete for the mass
market sales they would in the past have conceded
to rivals.
(A) they would in the past have conceded to rivals
(B) they would have conceded previously to their
rivals
(C) that in the past would have been conceded
previously to rivals
(D) it previously would have conceded to rivals in
the past
(E) it would in the past have conceded to rivals

I can go to oa withough understanding how "would have done" is used

pls explain the use of "would have done". I see this phrase only in past conditional sentence. I do not understand the use of this phrase in this sentence. I do not see the explantion of the use of this phrase in any grammar book. pls help