Identify the error in the sentence: "At age 85, Mr. Robinson's father, that had been the city mayor in the 1970's, now lives in Florida, with his dog Rico."

• A. At age 85
• B. City mayor in the 1970's
• C. Now lives in Florida
• D. No error

Answer: (B)

The correct identification of the error relates to the phrase "city mayor in the 1970's." The term "1970's" incorrectly uses an apostrophe, as it suggests possession rather than forming a plural. The proper way to indicate multiple years in a decade is simply to write "1970s" without the apostrophe. This maintains clarity that it's referring to the decade and avoids grammatical confusion regarding possession.

Therefore, the phrase indicates that the error involves grammatical usage regarding decade representation, making it clear why the option pointing out this mistake is the right choice. The other elements of the sentence do not contain similar issues, thus reinforcing the accuracy of the selected error.