Critical Reasoning (CR) | Manager: Our company's mail-order sales have recently increased

Manager: Our company's mail-order sales have recently increased 25 percent. This increase started around the time we started offering unlimited free shipping, rather than just free shipping on orders over $50. Thus, our change in policy probably caused the increase.

Which one of the following, if true, most strengthens the manager's argument?

(A) Mail-order sales have been decreasing for companies that do not offer unlimited free shipping.
(B) The company did not widely advertise its change in
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