AnjaliOberoi wrote:Subject here is computer company's troubles (plural) and attempts to is correct usage.

In option A, we can't use "it" because "it" is going to computer company's troubles, which is plural.
In option B, we have attempts at and so that is also not correct. i believe so is used in cases where we are concluding something....
C and E- Attempts at(wrong),usage of "them is also wrong" as it is refering to subject (trouble's) but usage is redundant
eg the car is of red colors and has 4 seats(correct)
the car is of red color and has 4 seats in it.(wrong)

D is correct

ceilidh.erickson wrote:Anjali is correct - we can't use "it" here, since "blunders" is plural.

To more specifically explain the difference between D and E, we need to examine subordinate clauses...

When we use the relative pronoun "that," we're creating a subordinate clause. Within the subordinate clause, we need a subject and a verb. Consider:

The book that is on the table is blue.
The book that you bought for me is blue.

In each of these examples, "that" begins a subordinate clause that modifies the noun "book." In the first example, the pronoun "that" is the subject of the subordinate clause, and the verb is "is."

In the second example, though, "you bought" is the subject and verb of the subordinate clause, and "that" is the object.

In the example sentence we're discussing,
that several attempts at revising corporate strategies have failed to correct them
the subject and verb are "attempts... have failed to correct." And what have attempts failed to correct? The managerial blunders - represented in this clause by the pronoun "that." The pronoun "that" is the object of the clause.

If we use "them" at the end of the clause as well, then it's redundant. We've used two different to function as the same object. That's why we shouldn't use "them," and the correct answer is D.