Surprisingly tough question for #3!
The conclusion is that offering free services to new customers is not an ideal business practice. Why not?
Because the majority of a bank's customers--the regular long-term ones--are excluded from such offers.
What's the gap? Well - can we say the practice is not ideal just because those folks are excluded? Maybe they don't care or notice? And maybe that's what's needed to attract new business. It seems like the premise is hinting at some sort of reaction by those folks, but we don't hear about it. So, maybe it's still an ideal practice.
(B) addresses that gap by pointing out that the real ideal practice is something else (offering perks to the most loyal customers).
(A) is out of scope - we're not comparing banks.
(C) is tempting, but it just helps explain why the practice being evaluated is more affordable than others. Even if we know (C) were true, it might be true that not offering any free services is the most ideal practice. Note that (C) doesn't really weaken the argument though it seems to: just because offering free services to everyone is too expensive doesn't mean that offering them to just new customers is the ideal practice.
(D) is oddly tempting. It tells us that folks tend to stick with their bank. Perhaps it's tempting because it seems like that mean that the old-timers don't care if the newbies get freebies - but if anything, that would weaken the argument! In the end, we don't care about how those folks behave - we want to know if the business practice is ideal or not.
(E) is also tempting - but if anything, it weakens. We want to hear that the practice is NOT ideal, not that it works sometimes. Also, "some" is pretty vague - is that two banks? And, are those banks offering those free service only to new customers?
#officialexplanation