OG11-5

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 it would in the past have conceded to rivals.

这里的定语从句的that省略了，请问这种省略有什么原则吗？

我也想知道，是定语从句吗？好像总是有这样的情况不过一时想不起来哪里见到了，有什么原则呢？

题目是

 5.As tis 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          选（E）
(E) it would in the past have conceded to rivals

We can usually leave out the relative pronoun "that" when it is the object in a relative clause.

for example:  Look!  There are the people (that) we met in Beijing.

   ... the mass market sales (that) it would in the past have conceded to rivals (E).

= ...the company would in the past have conceded the mass market sales to rivals

the mass market sales 是 that 从句中的宾语, 所以 "that" 可省略