这个是选D the name of which吧
句子的主干是 His boat is famous.
然后中间是有一个非限制性定语从句,来修饰这个boat,定语从句的先行词是boat
如果用B的话,应该是whose name, 因为whose代替了 the boat's
whose name = the boat's name 那艘小船的名字
His boat, whose name is topsail , is famous. 他的小船,名字为topsail的小船,很有名.
选择D是因为 the name of which里面的which是代替了the boat, 也就是相当于the name of the boat 船的名字
His boat,the name of which is topsail,is famous