Help analyzing a wrong answer

[gmat62k10]

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 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

D amounting to little less than half the population of the state,down from three quarters a decade ago

This question is straightforward and the OA is D. But the hard part was making a call between B and D. I can see a bunch of problems with B ,"down..", the second "they"...
Some additional analysis would be helpful

[shovan85]

Please edit the above post and submit the full question. This will help others as well. Thanks

In B "THAT" has ambiguous antecedent.

In D the usage of "amounting" correctly refers to the preceeding clause.

[uwhusky]

Unlike most grammar authority, GMAT doesn't like the usage of "that" for people.

[Jim@Grockit]

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 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

D amounting to little less than half the population of the state,down from three quarters a decade ago

This question is straightforward and the OA is D. But the hard part was making a call between B and D. I can see a bunch of problems with B ,"down..", the second "they"...
Some additional analysis would be helpful

"That" has an unclear referent; in common usage, it can even refer to the entire preceding clause ("He embezzled millions of dollars from the company; that's why they fired him.")

It's also a small consideration, but never forget that the GMAT's dislike of extra words is matched only by its undying love of parallelism: "and that amounts" is three words, and "amounting" is one.

[gmat_perfect]

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 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

D amounting to little less than half the population of the state,down from three quarters a decade ago

This question is straightforward and the OA is D. But the hard part was making a call between B and D. I can see a bunch of problems with B ,"down..", the second "they"...
Some additional analysis would be helpful

Look at another problem in B:

B 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

"Down from X", where X should be a number.

--> So B is wrong for using "Down from a decade ago".

Thanks.