题目内容：
根据以下内容，回答题。Summer Travel Sale
North Sun Airlines is proud to bring you its annual Summer Travel Sale!As usual，fights between selected cities in the U．S．and Canada are on sale for as low as $44 each way．Fares this low can’t last long，So visit our website or call a customer service operator and book your tickets today!
Prices below apply to travel beginning May 21st，2006．Travel must be completed by October 1st，2006．Tickets must be purchased by May 1st to be eligible for the sale．
Sample One-way Summer Sales Fares Minneapolis to Winnipeg$44 Pittsburgh to Toronto$64 Sacramento to Victoria$64 Omaha to Denver$94 Detroit to Ottawa$94
Cleveland to Toronto$94．Toronto to Dallas$94 Columbus to Quebec City$104
Philadelphia to Ottawa$104 San Jose to San Antonio$1 14
What is true about North Sun Airlines? A．It offers worldwide flights
B．It is based in the United States
C．It holds a sale every summer
D．It sells cheap round-trip tickets
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