分式$\frac{x}{3y}$与$\frac{3x}{2y^2}$的最简公分母是（　　）

任务型阅读

    A traveler came out of the airport. There were a lot of taxis. He asked every taxi driver his name. Then he took the third one. It cost 5 dollars from the airport to the hotel. "How much does it cost for the whole day?" The man asked. "100 dollars," said the taxi driver. This was very expensive, but the man said it was OK.

    The taxi driver took the man everywhere. He showed him all the parks and museums in the city. In the evening they went back to the hotel. The traveler gave the taxi driver 100 dollars and said, "What about tomorrow? It's another 100 dollars. "But the man said, "That's OK! See you tomorrow." The taxi driver was very pleased.

    The next day the taxi driver took the traveler everywhere again. They visited all the parks and museums again, and in the evening they went back to the hotel. The man gave the taxi driver 100 dollars again and said, "I'm going home tomorrow." The taxi driver was sorry because he liked the traveler and, above all, 100 dollars a day was a lot of money. "So you're going home. Where do you come from?" he asked. "I come from New York!" said the traveler. "I have a sister in New York. Her name is Susanna.  Do you know her?" "Of course I know her. She gave me 200 dollars for you! "

下列各组中的离子，能在溶液中大量共存的有