How can Nike tie its increase in sales directly to the Kaepernick advertisements?

a. Other similar celebrity campaigns produced similar results.
b. The sales increased suddenly and dramatically days afterwards.
c. The fact that many burned Nike gear meant that they had to replace it.
d. The marketing budget had been increased, so it must be more effective.

b. The sales increased suddenly and dramatically days afterwards.

The most direct and clear indication that Nike's increase in sales can be tied to the Kaepernick advertisements is the significant and immediate spike in sales that occurred shortly after the campaign was launched. This suggests a direct correlation between the ad campaign and increased consumer interest and purchases.