Given the task definition and input, reply with output. In this task, you're given a question, a context passage, and four options which are terms from the passage. After reading a passage, you will get a brief understanding of the terms. Your job is to determine by searching and reading further information of which term you can answer the question. Indicate your choice as 'a', 'b', 'c', or 'd'. If you think more than one option is plausible, choose the more probable option to help you answer the question.

Question: How old was the engineer who built Fort Mercer when it was built? Passage:Fort Mercer was a fort on the Delaware River in New Jersey constructed by the Continental Army during the American Revolutionary War. Built by Polish engineer Thaddeus Kosciuszko under the command of George Washington, Fort Mercer was built in 1777 to block the approach to Philadelphia, Pennsylvania in concert with Fort Mifflin on the Pennsylvania side. Fort Mercer was located in an area called Red Bank, in what is now the borough of National Park, Gloucester County, New Jersey. The fort was named in honor of Brigadier General Hugh Mercer who had died earlier that year at the Battle of Princeton. The fort's site is now part of Red Bank Battlefield Historical Park, which includes a monument and museum. Several cannons attributed to British warships lost supporting the attack on the fort, and others found buried at the fort itself, are in the park.
Links: a. Hugh Mercer b. Tadeusz Kosciuszko c. American Revolutionary War d. Tadeusz Kosciuszko
b