recent finding lend strong support to the theory ( that a black hole lies at the center of the MILK WAY and of) many of the 100 billion other galaxiers estimated to exist in the universe
a 不变
d. of a black hole lying at the MILKY WAY's center and
1.of结构后面跟doing的表达式属于繁琐的结构。有效性不如A好 2.milk way非生物用's格式不好 3.原句的意思是center of many of the 100 billion other galaxiers estimated to exist in the universe,D没有表达出这个意思,改变了句意。