A. You flip the coin 25 times and observe 13 heads, then the probability to get head is 13/25 (very close to theoretical probability 1/2).
B. You flip the coin and observe 4 consecutive heads. This statement may occur to be true, because next 4 could be consecutive tails.
C. You flip the coin 10 times and observe 8 heads, then the probability to get head is 8/10=4/5.
D. You flip the coin 100 times and observe 72 heads, then the probability to get head is 72/100=18/25.
Since 1/2<18/25<4/5, you can conclude that the best evidence that the coin is unfair provides statement C.
Answer: correct choice is C.