In this task, based on the given input, we ask you to write a question about when an event happened. Your question should be answerable with common knowledge on when events usually take place. For example, "going to school" usually happens during the day (not at 2 A.M). Don't create questions which have explicit mentions of answers in the text. Instead, it has to be implied from what is given. In other words, we want you to use "instinct" or "common sense". The written questions are not required to have a single correct answer.

Sentence: One result was two NSC-led interagency trips to Persian Gulf states in 1999 and 2000.
When did the NSC arrive at the Persian Gulf in 1999?