下列（）环的保护通道不是空闲的（不传额外业务）。A.两纤单向通道环 B.两纤双向复用
题型：单项选择题
问题：
下列（）环的保护通道不是空闲的（不传额外业务）。
A.两纤单向通道环
B.两纤双向复用段环
C.四纤双向复用段环
D.两纤单向复用段环
题型：单项选择题
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| Marianne, a schoolgirl, was learning to play the piano, and day after day her father stood behind her as she practiced. How very patient and loving 1 was, and how cleverly he showed Marianne 2 to play some difficult pieces! She was making progress, and that was excellent. And there, almost last in the big chair, sat Wolfgang, her four-year-old 3 , who never had to be told to 4 quiet when Marianne was 5 . One evening at sundown the father patted Marianne's shoulder, 6 she had dome very well. At the moment Wolfgang climbed on his father's knee and begged to play the pretty 7 Marianne had now mastered. What a 8 that was! Picking his baby son, the father 9 , tapped the nose and said, "Look at your small 10 . You must wait, like man. You must wait!" There was no end, and Marianne had to tell her mother about Wolfgang wanting to 11 one of the classics. After 12 Marianne helped clear away the dishes when the father lit his pipe (烟斗). But the pipe went out. He was on his feet. "Listen! Marianne is playing that piece 13 than ever!" But Marianne was washing pots in the kitchen. His wife following, he went up  stairs, the lamp in one hand, his pipe in 14 ,he pushed open the door, and there was little Wolfgang 15 in the darkness. "I love it so!" whispered the child. It was the beginning of Mozart's life of music. | ||||
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