After living in the United States for quite a long time, I do not think about the cultural differences any more. Last month, my parents came to visit me. Their observations   on the American lifestyle reminded me that cultural differences between living in China and America are actually everywhere. When my parents came to America, they praised my house. Everyone had his/her own bedroom; there was a front yard, a backyard and a garage; there were many bathrooms - all convenient and comfortable. However, they were not used to the glass doors at the first floor. My mom, from southern China, was worried that someone would break open the glass doors. Though I said that nobody would do that, she was still worried about it. When I brought them to eat in fast food restaurants, whether it was in McDonald's or KFC, they saw that refilling drinks was for free. This concept   of free refill was so new to them. A Chinese friend told me a story. He and his American girlfriend ate at a restaurant. His girlfriend wanted to drink English tea. He was curious, so he tried some and found that it didn't taste bad with milk and sugar in it. Adding more water to tea is free of course, so he drank more cups. His girlfriend found it embarrassing and explained to him that what he was doing was not exactly fair. If he wanted to drink more tea, he should buy another cup. My friend thought that Americans could take advantage of the free refills, but only a few of them did that. After staying in America for some time, he changed his habit. When eating at McDonald's for the first time in America, the writer's parents were probably surprised that   _  .
there were so many choices the prices for food were so low they could refill drinks for free they could get extra food for free
Question: After living in the United States for quite a long time, I do not think about the cultural differences any more. Last month, my parents came to visit me. Their observations   on the American lifestyle reminded me that cultural differences between living in China and America are actually everywhere. When my parents came to America, they praised my house. Everyone had his/her own bedroom; there was a front yard, a backyard and a garage; there were many bathrooms - all convenient and comfortable. However, they were not used to the glass doors at the first floor. My mom, from southern China, was worried that someone would break open the glass doors. Though I said that nobody would do that, she was still worried about it. When I brought them to eat in fast food restaurants, whether it was in McDonald's or KFC, they saw that refilling drinks was for free. This concept   of free refill was so new to them. A Chinese friend told me a story. He and his American girlfriend ate at a restaurant. His girlfriend wanted to drink English tea. He was curious, so he tried some and found that it didn't taste bad with milk and sugar in it. Adding more water to tea is free of course, so he drank more cups. His girlfriend found it embarrassing and explained to him that what he was doing was not exactly fair. If he wanted to drink more tea, he should buy another cup. My friend thought that Americans could take advantage of the free refills, but only a few of them did that. After staying in America for some time, he changed his habit. When eating at McDonald's for the first time in America, the writer's parents were probably surprised that   _  .
A. there were so many choices
B. the prices for food were so low
C. they could refill drinks for free
D. they could get extra food for free
Answer: