我也有一道老题

jeannette

一道老题，其他选项明显错，就不说了，但正确答案里有一个语法点不懂
As a result of the ground-breaking work of Barbara McClintock, many scientists now believe that all of the information encoded in the 50,000 to 100,000 different genes found in a human cell is contained in a mere three percent of the cell’s DNA.
a mere three percent of the cell’s DNA为什么要加a？
好象抽象名词可以用: a 5 percent increase, 这里three percent of the cell’s DNA也可以用吗？多谢！[em13]

princess

sigh 偶搞不定呃

哪位高人指点啊

tongxun

a 在这里的用法可能是泛指某类物质。