Choose the best word to paraphrase the underlined part. 
The little boat moves from side to side in the water.

A. 西湖白堤的得名与李白有关
B. 古代男子到十五岁行“冠礼”
C. “十八般武艺”是指十八个武术流派
D. 古人以九为阳，所以九月初九为重阳