Answer:
C. flank
Step-by-step explanation:
A flank attack refers to an act by a product company whereby it attacks the weak links in the products of it's major competitor, particularly a leader.
In such scenarios, the company observes the limitations of the competitor's products and then embodies them in it's own new similar product. In a flank attack, the two companies deal in similar products which can be substituted for one another.
In the given case, Colgate came out with a similar product with improved aspect which it's major competitor's product overlooked i.e dental sensitivity aspect. This represents a case of flank attack.