With Proposition 13, if you bought your house 11 years ago for $75,000

D says:
"If Proposition 13 is not repealed, identical properties will continue to be taxed at different rates."

In the given stem, we have no proof of this statement. We have the word identical property being bought at a different rate but there is another factor next to it. One preoperty was bought 11 years and another identical property was bought this year. Hence even the time the house was bought is a factor involved and hence we cannot assume the if Proposition 13 is not repealed, it would tax identical properties at different rates!

And if you are considering the last statement as the bases for this answer, this won't be correct. As per last statement - "Without Proposition 13, both you and your neighbor would pay $6,000 a year in property taxes" it means
If No Proposition 13 ....... then Same Tax
But this doesn't mean that below statement is TRUE:
If Proposition 13.... then DIFF TAX.... - This cannot be true! Imagine if you and your neighbour have the same property. Even with Proposition 13 rule, you would pay same Tax.

Hence D is wrong...

B says - "If Proposition 13 is repealed, every homeowner is likely to experience a substantial increase in property taxes."
This is but obvious as the same is given in the stem. With Proposition, the tax would be $2,000. And if no Proposition then the tax would be $6,000... This would hold good for any property since with Proposition 13 it would be 1% of Property value of the first yr and without Proposition 13 it would be 3% of the property value