Your question is incomplete because you have not provided the answer options, which are:
data, to support the claim that user-acquisition costs are rising quickly
quotation, to cite an expert opinion
fact, to support the claim that mobile users are loyal
definition, to explain what user-acquisition cost means
Answer:
data, to support the claim that user-acquisition costs are rising quickly
Step-by-step explanation:
Sentence two from "Video Games in the Age of Cell Phones" supports the information given in the topic sentence, which is number one. Thus, sentence two provides statistical numbers as evidence to prove that advertising costs have risen faster than profits. In that respect, it mentions that Fiksu claims to have spent $2.74 to gain a customer, a cost which is eighty per cent more expensive than the year before.