At the annual stockholders meeting, investors heard a

sudeep
but "which" refers to company here, doesn't it?

'numerous challenges (facing the company)' - Noun Phrase
'facing the company' is a participle modifier for the noun challenges.
which is modifying that noun phrase,i.e., challenges.

Please correct me if I am wrong!

Yes ..which should refer to the company..in option (B)...Option D..seems to be the right one..OA plzz

Can someone please confirm this!

Thanks a lot guys, OA is D

Option B
B. which includes the threat of a rival's multibillion-dollar patent-infringement suit and (the)declining sales of

Here "the" should be added with 'declining sales'

M I correct?

Agreed, trying to make noun parallel with complex gerund.
But I think "which" is also incorrectly placed, as "company" is the closest noun.

guys, I have one more confusion.

shouldn't we have a verb like "include" before the sentence in option D
"among them the threat of a rival's multibillion-dollar patent-infringement suit and the decline in sales of...."

What I feel is that without verb "include" the sentence becomes fragmented

"which" doesn't have to always refer to nearest noun, in most cases it does, but there are exceptions...I agree with sudeep...

Here is an example where 'which' is fine in (b):

Although she had been known as an effective legislator first in the Texas Senate and later in the United States House of Representatives, not until Barbara Jordan's participation in the hearings on the impeachment of President Richard Nixon in 1974 was she made a nationally recognized figure, as it was televised nationwide.

A. later in the United States House of Representatives, not until Barbara Jordan's
participation in the hearings on the impeachment of President Richard Nixon in
1974 was she made a nationally recognized figure, as it was
B. later in the United States House of Representatives, Barbara Jordan did not
become a nationally recognized figure until 1974, when she participated in the
hearings on the impeachment of President Richard Nixon, which were
C. later in the Untied States House of Representatives, it was not until 1974 that
Barbara Jordan became a nationally recognized figure, with her participation in
the hearings on the impeachment of President Richard Nixon, which was
D. then also later in the United States House of Representatives, not until 1974 did
Barbara Jordan become a nationally recognized figure, as she participated in the
hearings on the impeachment of President Richard Nixon, being
E. then also later in the United States House of Representatives, Barbara Jordan did
not become a nationally recognized figure until 1974, when she participated in the
hearings on the impeachment of President Richard Nixon, which was

WHICH represents a sentence in this case, and it's not allowed in GMAT grammar.

This is not as daunting a question as it appears. The decision point is easy "sales for" is an incorrect idiom. The correct idiom is "sales of"

1) Including among them the threat from a rival’s multibillion-dollar patent-infringement suit and the declining sales for
WRONG :- Incorrect idiom "sales for" is incorrect ; "sale of" is correct idiom

2) Which includes the threat of a rival’s multibillion-dollar patent-infringement suit and the declining sales of
WRONG:- "which" is incorrectly modifying company. "which" should modify challenges

3) Included among these the treat from a rival’s multibillion-dollar patent-infringement suit as well as a decline in sales for
WRONG :- Incorrect idiom "sales for" is incorrect ; "sale of" is correct idiom

4) Among them the treat of a rival’s multibillion-dollar patent-infringement suit and the decline in sales of
CORRECT:- Correct idiom; crisp and concise.

5) Among these the treat from a rival’s multibillion-dollar patent-infringement suit as well as the decline in sales for
WRONG :- Incorrect idiom "sales for" is incorrect ; "sale of" is correct idiom