Final answer:
The United States first participated in the Davis Cup in 1900, which is not among the answer choices provided. The tournament itself is an international team tennis event that began after 1899.
Step-by-step explanation:
The first time the United States participated in the Davis Cup as a member was in the year 1900. None of the answer choices provided (1963, 1968, 1972, 1975) correspond to the United States' first participation year. The Davis Cup is an international team event in men's tennis, which was first conceived in 1899 by four members of the Harvard University tennis team who wanted to set up a match between the USA and Great Britain. After the initial challenge, the event became a regular one, with other nations joining over the years.