Context: On July 25, 2015, the 18th and 19th satellites were successfully launched from the Xichang Satellite Launch Center, marking the first time for China to launch two satellites at once on top of a Long March 3B/Expedition-1 carrier rocket. The Expedition-1 is an independent upper stage capable of delivering one or more spacecraft into different orbits.

Question: When were the 18th and 19th satellites for the BeiDou system launched?
Answer: July 25, 2015

Question: Where were the 18th and 19th satellites for the BeiDou system launched from?
Answer: the Xichang Satellite Launch Center

Question: What were the 18th and 19th satellites for the BeiDou system launched with?
Answer: Long March 3B/Expedition-1 carrier rocket

Question: What is the Expedition-1?
Answer: an independent upper stage capable of delivering one or more spacecraft into different orbits

Question: During which month of 2007 was the 18th satellite launched?
Answer: Unanswerable

Question: During which month of 2017 was the 19th satellite launched?
Answer: Unanswerable

Question: In which year was the 20th satellite launched?
Answer: Unanswerable

Question: Where were the 2nd and 3rd satellites launched from?
Answer: Unanswerable

Question: This marked the third time China launched how many satellites at once? 
Answer: Unanswerable