Answer:
4- A ridiculously high number of illegal immigrants are caught at the border every day.
Step-by-step explanation:
Remember that something that is biased is showing unreasonable like or dislike for something based on personal opinion, in other words, it tends to be subjective. In this case, all sentences, except the number 4, are telling us facts. They present the information as they found it, without any emotional charge, they limit themselves to present the data and information given by authorities. The fourth sentence uses the word "ridiculously" which shows us that the author has already taken a position towards the issue, the authors think that the amount of immigrants caught is unreasonable high, expressing an opinion.