GWD1-23

For the first time in the modern era, non-Hispanic Whites are officially a minority in California,
which amounts to a little less than half the population of the state, down from nearly three-quarters only a decade ago.

b) which amounts to a little less than half the poputation of the state, down from a decade ago, when it was nearly three-quaters

c)...

d) amounting to  a little less than half the population of the state, down from nearly three-quaters a decade ago.

正确为d.  我选了a。 请教能人，a为什么不对?  which 在此能不能修饰minority?  先谢了！！

Q23:

For the first time in the modern era, non-Hispanic Whites are officially a minority in California, which amounts to a little less than half the population of the state, down from nearly there-quarters only a decade ago.

1. which amounts to a little less than half the population of the state, down from nearly three-quarters only a decade ago
2. which amounts to a little less than half the population of the state, down from a decade ago, when it was nearly three-quarters
3. and that amounts to a little less than half the population of the state, down from a decade ago, when they were nearly three-quarters
4. amounting to a little less than half the population of the state, down from nearly three-quarters a decade ago
5. amounting to a little less than half the population of the state, down from what it was a decade ago by nearly three-quarters

E为什么不对？意思上应该是降了3/4？