Your thoughts on this

[vidyagattu]

Planned reduction in orders for components for the iPhone 5 is due to weaker-than-expected demand because Apple’s share of world-wide smartphone shipments have declined from 23% to 14% since the last year while Samsung’s share has steadily increased from 8.8% to 31% during the same time period.

A. due to weaker-than-expected demand because Apple’s share of world-wide smartphone shipments have declined

B. because of weaker-than-expected demand: Apple’s share of world-wide smartphone shipments declined

C. due to weaker-than-expected demand: Apple’s share of world-wide smartphone shipments has declined

D. because of weaker-than-expected demand, declining Apple’s share of world-wide smartphone shipments

E. because of weaker-than-expected demand that decreased Apple’s share of world-wide smartphone shipments

This is a question found on gmatclub.com.
My doubt :
For this question, OA is C.But, I was advocated this blind(ofcourse, it makes sense) rule on some other forum.
"Here is the short rule you need to remember – on the GMAT if you ever get a split between due to and because of, blindly go with because of. No matter what the rule says, it will ALWAYS be because of that will be correct (the sentence will obviously be constructed in such a manner as to make this correct)."
Pls confirm the validity of this.Thanks.

[tim]

As per the forum rules, we need a verifiable source for the problem before we can deal with this question (gmatclub is a repository for problems from other sources; it is not a source itself). If the question is not one of ours or one that is copyright-free, we will have to delete the question.

[RonPurewal]

That "rule" is not a rule.

In this question, "due to" is correct, and "because of" is incorrect.

But, as Tim noted, we can't discuss details without a citation of the original source.

[RonPurewal]

By the way——If you ever see "Don't ever pick this group of words!!", that's pretty much never going to be a real rule. Some of these "rules" are decent guessing methods, but that's all they should be——guessing methods.

Yes, there are pairs of words that are incompatible with each other (mostly common idioms, e.g., more ... than ... is correct while more ... as ... is incorrect).
To find such errors, though, you'll have to connect the two parts across some distance (and, in most cases, across a certain quantity of intervening "junk").

[RonPurewal]

Also, it's worth noting that the GMAC people do read internet forums, too (horrors!)——and that they very well might adjust the content of the exam accordingly, to penalize people who are memorizing such non-rules as this one.

E.g., back in the OG10 days, basically all of the OG answer choices with "being" were incorrect, and almost all of the choices written in passive voice were incorrect, too.
So, a bunch of people wrote "NEVER pick 'being' or passive" on forums.
Sure enough, in the following editions of the OG and GMATPrep, shazam!, appeared correct sentences with "being" and passive verbs.
Something tells me this wasn't a coincidence.