HOT Competition: A large manufacturing firm, on average, offers a high

As the question is written, it has no right answer, so I wouldn't worry about it much. Answer B is not right, because the stem tells us that the company "offers a higher compensation to skilled employees than to unskilled ones". That is a premise of the argument; it cannot be wrong (the "official explanation" seems to completely miss this point). The reason they offer more compensation to skilled workers is thus irrelevant, because we know for a fact that they do offer higher compensation to skilled workers. So B is not a necessary assumption - maybe the company does only pay skilled workers more because of their scarcity, but maybe the company won't hire enough skilled workers to meaningfully address that scarcity, say, and the pay discrepancy will continue.

But C is not a good answer either. The stem compares the present with the future: the company will hire skilled workers and the average salary "will increase". Answer C compares the present with the past: " The percentage of skilled employees is higher now than it had been the previous year in that firm." We don't care about how things changed from last year to this one. We care how things are going to change during this year, after the hirings that have not yet happened. So C is irrelevant, as it's worded.

It's also easily possible for the average salary to rise even if the proportion of skilled workers drops. Maybe the company will give every employee an enormous raise, skilled or not. Then the average salary will go up no matter who they hire. So C doesn't need to be true for the conclusion to be true, and I'm not sure I'd agree that the argument "depends" on C (assuming C used the right verb tenses). The conclusion certainly doesn't depend on C, though if you don't assume C the specific logic of the argument becomes meaningless.

Can someone explain why C is the correct answer? Based on the passage, I thought that the firm plans to hire more skilled workers this year which hasn't happened yet. Yet C assumes that the hiring has already happened.